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25 pages, 7449 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydrogen Production via Pd-TiO₂ Photocatalytic Water Splitting under Near-UV and Visible Light: Analysis of the Reaction Mechanism

by Bianca Rusinque, Salvador Escobedo and Hugo de Lasa

Catalysts 2021, 11(3), 405; https://doi.org/10.3390/catal11030405 - 23 Mar 2021

Cited by 43 | Viewed by 8914

Abstract

Photocatalytic hydrogen production via water splitting using a noble metal on a TiO₂ is a technology that has developed rapidly over the past few years. Specifically, palladium doped TiO₂ irradiated with near-UV or alternatively with visible light has shown promising results. [...] Read more.

Photocatalytic hydrogen production via water splitting using a noble metal on a TiO₂ is a technology that has developed rapidly over the past few years. Specifically, palladium doped TiO₂ irradiated with near-UV or alternatively with visible light has shown promising results. With this end in mind, strategically designed experiments were developed in the Photo-CREC Water-II (PCW-II) Reactor using a 0.25 wt.% Pd-TiO₂ under near-UV and visible light, and ethanol as an organic scavenger. Acetaldehyde, carbon monoxide, carbon dioxide, methane, ethane, ethylene, and hydrogen peroxide together with hydrogen were the main chemical species observed. A Langmuir adsorption isotherm was also established for hydrogen peroxide. On this basis, it is shown that pH variations, hydrogen peroxide formation/adsorption, and the production of various redox chemical species provide an excellent carbon element balance, as well as OH^• and H^• radicals balances. Under near-UV irradiation, 113 cm³ STP of H₂ is produced after 6 h, reaching an 99.8% elemental carbon balance and 99.2% OH^• and H^• and radical balance. It is also proven that a similar reaction network can be considered adequate for the photoreduced Pd-TiO₂ photocatalyst yielding 29 cm³ STP of H₂ with 95.4% carbon and the 97.5% OH^•–H^• radical balance closures. It is shown on this basis that a proposed “series-parallel” reaction network describes the water splitting reaction using the mesoporous Pd-TiO₂ and ethanol as organic scavenger. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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14 pages, 3434 KiB

Open AccessArticle

Scaling up a Gas-Phase Process for Converting Glycerol to Propane

by Christian Hulteberg and Andreas Leveau

Catalysts 2020, 10(9), 1007; https://doi.org/10.3390/catal10091007 - 3 Sep 2020

Cited by 3 | Viewed by 3144

Abstract

It is of interest to study not only the fundamental behavior of catalysts and reactors but also to ensure that they can be scaled up in size. This paper investigates the scale-up of a glycerol-to-propane process starting from fundamental laboratory data from micro-reactor [...] Read more.

It is of interest to study not only the fundamental behavior of catalysts and reactors but also to ensure that they can be scaled up in size. This paper investigates the scale-up of a glycerol-to-propane process starting from fundamental laboratory data from micro-reactor testing to the kilogram scale. The process is described in detail and consist of the use of design documents and computer simulations for determining the sizes of the unit operations involved. The final design included a vaporizer section for a glycerol/water mixture, four reactors in tandem with subsequent dehydration and hydrogenation reactions, a flash vessel to separate the excess hydrogen used, and a compressor for recycling the excess hydrogen with additional light components. The system was commissioned in a linear fashion, which is described, and operated for more than 3000 h and more than 1000 h in the final operating mode including recycle. The major results were that no catalyst deactivation was apparent aside from the slow build-up of carbonaceous material in the first dehydration reactor. That the system design calculations proved to be quite close to the results achieved and that the data generated is believed to be sufficient for up-scaling the process into the 1000 to 10,000 tonnes-per-annum range. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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19 pages, 7771 KiB

Open AccessArticle

Hydrogenation of Furfural to Furfuryl Alcohol over Ru Particles Supported on Mildly Oxidized Biochar

by Raoof Bardestani, Rouholamin Biriaei and Serge Kaliaguine

Catalysts 2020, 10(8), 934; https://doi.org/10.3390/catal10080934 - 13 Aug 2020

Cited by 13 | Viewed by 4194

Abstract

Catalytic hydrogenation of aldehydes is required as the stabilizing step in bio-oils conversion. Ruthenium supported on carbon was used in the present work for hydrogenation of furfural (FF) to furfuryl alcohol (FA). Converting a biochar with no surface area and low carboxyl groups [...] Read more.

Catalytic hydrogenation of aldehydes is required as the stabilizing step in bio-oils conversion. Ruthenium supported on carbon was used in the present work for hydrogenation of furfural (FF) to furfuryl alcohol (FA). Converting a biochar with no surface area and low carboxyl groups surface density to an outstanding catalyst support using a very simple mild air/steam oxidation is the original contribution of this work. The mildly oxidized biochar is impregnated with a targeted loading of 2.5 wt.% Ru via ion-exchange, using

Ru {({NH}_{3})}_{6} {Cl}_{2}

precursor. ICP analysis shows that the mild oxidation increases Ru adsorption capacity of untreated biochar from 1.2 to 2.2 wt.%.

H_{2}

chemisorption and TEM analysis indicate that the preliminary mild oxidation leads to higher Ru dispersion. XPS analysis also shows that the treatment prevents Ru from surface segregation. The highest value of 93% FA selectivity at 53% FF conversion was obtained in a batch autoclave reactor under optimized conditions. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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10 pages, 3284 KiB

Open AccessArticle

Mechanistic Investigation on Hydrocyanation of Butadiene: A DFT Study

by Kaikai Liu, Shuai Zhang and Minghan Han

Catalysts 2020, 10(8), 818; https://doi.org/10.3390/catal10080818 - 22 Jul 2020

Cited by 1 | Viewed by 5488

Abstract

The nickel-catalyzed addition of Hydrocyanic acid (HCN) to butadiene usually leads to a mixture of the branched 2-methyl-3-butenenitrile (2M3BN) and the linear 3-pentenenitrile (3PN) with a 30:70 ratio by employing mono-dentate phosphites, while a 97% selectivity to 3PN is obtained using a 1,4-bis(diphenyphosphino)butane [...] Read more.

The nickel-catalyzed addition of Hydrocyanic acid (HCN) to butadiene usually leads to a mixture of the branched 2-methyl-3-butenenitrile (2M3BN) and the linear 3-pentenenitrile (3PN) with a 30:70 ratio by employing mono-dentate phosphites, while a 97% selectivity to 3PN is obtained using a 1,4-bis(diphenyphosphino)butane (dppb) ligand and Ni(COD)₂ (1,5-Cyclooctadiene) as catalysts. To explain this phenomenon, a reasonable mechanism of the hydrocyanation, involving the cyano (CN) migration (for 3PN) and the methylallyl rotation (for 2M3BN) pathways, is proposed. The key intermediates and the rate-determining steps in the pathways have been illustrated. The methylallyl rearrangement is the rate-determining step in the formation of 3PN while the reductive elimination governs the reaction to 2M3BN, which is subsequently isomerized to 3PN. Moreover, the opposite changes of the bite angle of the intermediates and transition states explain how the reactions proceed in two different directions. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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27 pages, 7861 KiB

Open AccessFeature PaperArticle

An Eco-Friendly Fluidizable Fe_xO_y/CaO-γ-Al₂O₃ Catalyst for Tar Cracking during Biomass Gasification

by Cindy Torres, Samira Rostom and Hugo de Lasa

Catalysts 2020, 10(7), 806; https://doi.org/10.3390/catal10070806 - 20 Jul 2020

Cited by 18 | Viewed by 3966

Abstract

The present study deals with the development, characterization, and performance evaluation of an eco-friendly catalyst, using 2-methoxy-4-methylphenol (2M4MP) as a surrogate tar. The 2M4MP was selected due to its chemical functionalities and the fact that it is a good model compound to represent [...] Read more.

The present study deals with the development, characterization, and performance evaluation of an eco-friendly catalyst, using 2-methoxy-4-methylphenol (2M4MP) as a surrogate tar. The 2M4MP was selected due to its chemical functionalities and the fact that it is a good model compound to represent the tar formed during biomass low temperature gasification. The eco-friendly catalyst was prepared using the typical Fe and Ca minerals which are present in ash. These ash components were added to a fluidizable γ-Al₂O₃ support using a multistep incipient impregnation, yielding Fe oxides as an active phase and CaO as the promoter. The prepared catalyst displayed a 120 m²/g BET specific surface area, with few γ-Al₂O₃ bulk phase changes, as observed with XRD. TPD-NH₃ and pyridine FTIR allowed us to show the significant influence of CaO reduced support acidity. A TPR analysis provided evidence of catalyst stability during consecutive reduction–oxidation cycles. Furthermore, catalyst evaluation vis-à-vis catalytic steam 2M4MP gasification was performed using the fluidized CREC riser simulator. The obtained results confirm the high performance of the developed catalyst, with 2M4MP conversion being close to 100% and with selectivities of up to 98.6% for C1-C2 carbon-containing species, at 500 °C, with a 7.5 s reaction time and 1.5 g steam/g 2M4MP. These high tar conversions are promising efficiency indicators for alumina catalysts doped with Fe and Ca. In addition, the used catalyst particles could be blended with biochar to provide an integrated solid supplement that could return valuable mineral supplements to the soil. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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15 pages, 1848 KiB

Open AccessArticle

Parametric Sensitivity Analysis for the Industrial Case of O-Xylene Oxidation to Phthalic Anhydride in a Packed Bed Catalytic Reactor

by Santiago Zuluaga-Botero, Izabela Dobrosz-Gómez and Miguel-Ángel Gómez-García

Catalysts 2020, 10(6), 626; https://doi.org/10.3390/catal10060626 - 4 Jun 2020

Viewed by 4573

Abstract

The operation of packed bed tubular reactors, for exothermic catalytic reactions, presents special challenges provoked by hotspot development. Their potential safety risk can be assessed using different mathematical methodologies, among them, the so-called parametric sensitivity analysis (PSA). This study deals with the identification [...] Read more.

The operation of packed bed tubular reactors, for exothermic catalytic reactions, presents special challenges provoked by hotspot development. Their potential safety risk can be assessed using different mathematical methodologies, among them, the so-called parametric sensitivity analysis (PSA). This study deals with the identification of safe operational conditions (e.g., feed temperature conditions) for the catalytic oxidation of o-xylene. Three different reaction networks, with different degrees of complexity, were analyzed. Thus, the critical values of the operating parameters, allowing us to define run-away and stable operation conditions, were provided for different reactive configurations. The obtained results were compared with the data reported by various authors who used similar reaction rate laws. The purpose of the present study is to illustrate the peculiarities of the PSA and its application for the design, analysis, and operation of o-xylene multitubular catalytic reactor. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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18 pages, 3497 KiB

Open AccessArticle

Structure, Acidity, and Redox Aspects of VOx/ZrO₂/SiO₂ Catalysts for the n-Butane Oxidative Dehydrogenation

by José-Luis Sánchez-García, Brent E. Handy, Ilse N. Ávila-Hernández, Angel G. Rodríguez, Ricardo García-Alamilla and Maria-Guadalupe Cardenas-Galindo

Catalysts 2020, 10(5), 550; https://doi.org/10.3390/catal10050550 - 15 May 2020

Cited by 5 | Viewed by 3394

Abstract

ZrOx/SiO₂ and VOx/ZrO_x/SiO₂ catalysts (5 wt %–25 wt % Zr, 4 wt % V) were prepared by grafting zirconium and vanadium alkoxides on Aerosil 380. All samples were characterized by temperature programmed reduction, N₂ physisorption, X-ray diffraction, Raman [...] Read more.

ZrOx/SiO₂ and VOx/ZrO_x/SiO₂ catalysts (5 wt %–25 wt % Zr, 4 wt % V) were prepared by grafting zirconium and vanadium alkoxides on Aerosil 380. All samples were characterized by temperature programmed reduction, N₂ physisorption, X-ray diffraction, Raman spectroscopy, and ammonia adsorption microcalorimetry. Tetragonal ZrO₂ and zircon (ZrSiO₄) were present at 25 wt % Zr, but only amorphous zirconia overlayer existed for lower loadings. At lower Zr loadings (5 wt %–10 wt % Zr), exposed silica surface leads to V₂O₅ crystallites and isolated VO₄ species, although V reducibility behavior changes, from being similar to VOx/SiO₂ (5 wt % Zr) to showing VOx/ZrO₂ behavior at 10 wt % Zr, and a diminished total amount of reducible V. Highly acidic ZrO₂ sites are covered by the vanadium grafting, forming weaker sites (60–100 kJ/mol NH₃ adsorption strength). Catalytic conversion and selectivity for the oxidative dehydrogenation of n-butane (673 K, n-C₄/O₂ = 2.2) over VOx/ZrOx/SiO₂ show that 1,3-butadiene is favored over cis-2-butene and trans-2-butene, although there is some selectivity to the 2-butenes when VOx/ZrO₂ behavior is evident. At low Zr loadings, butadiene formed during reaction acts as the diene species in a Diels–Alder reaction and gives rise to a cyclic compound that undergoes further dehydrogenation to produce benzaldehyde. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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15 pages, 3994 KiB

Open AccessArticle

Nanostructured Magnéli-Phase W₁₈O₄₉ Thin Films for Photoelectrochemical Water Splitting

by A. K. Mohamedkhair, Q. A. Drmosh, Mohammad Qamar and Z. H. Yamani

Catalysts 2020, 10(5), 526; https://doi.org/10.3390/catal10050526 - 10 May 2020

Cited by 21 | Viewed by 3964

Abstract

Converting water into hydrogen through the photo-electrochemical (PEC) process is one of the most exciting approaches in this field, and there is a quest to design or search for new electro-photo-catalytic materials. In this work, simple steps for fabrication and transformation of metallic [...] Read more.

Converting water into hydrogen through the photo-electrochemical (PEC) process is one of the most exciting approaches in this field, and there is a quest to design or search for new electro-photo-catalytic materials. In this work, simple steps for fabrication and transformation of metallic tungsten thin film into the photo-active Magnéli-phase (W₁₈O₄₉) of tungsten oxide thin film is demonstrated. The post-annealing temperature has a significant impact on the phase evolution of tungsten film into W₁₈O₄₉. The film thickness of W₁₈O₄₉ is controlled by controlling the sputtering time (or deposition time) of W film. The PEC performance of the as-prepared electrodes is evaluated by monitoring the water oxidation reaction under visible radiation. The PEC findings reveal a correlation between PEC performance and phase, morphology, and thickness of the film. The as-derived W₁₈O₄₉ can efficiently catalyze the water oxidation reaction at neutral solution pH, generating 0.6 and 1.4 mA cm⁻¹ photo-current at 0.6 and 0.8 V vs. Saturated calomel electrode (SCE), respectively, in addition to excellent stability. The electrical conductivity and the charge transfer kinetics are investigated employing the electrochemical impedance spectroscopic (EIS) technique. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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8 pages, 2280 KiB

Open AccessArticle

Carbon Formation at High Temperatures (550–1400 °C): Kinetics, Alternative Mechanisms and Growth Modes

by Luís Sousa Lobo and Sónia A. C. Carabineiro

Catalysts 2020, 10(5), 465; https://doi.org/10.3390/catal10050465 - 25 Apr 2020

Cited by 6 | Viewed by 3304

Abstract

This Note aims at clarifying the alternative mechanisms of carbon formation from gases at temperatures above 550 °C. Both the growth of carbon nanotubes (CNTs) by a hybrid route, and of graphene layers deposition by a pyrolytic route are analyzed: the transition had [...] Read more.

This Note aims at clarifying the alternative mechanisms of carbon formation from gases at temperatures above 550 °C. Both the growth of carbon nanotubes (CNTs) by a hybrid route, and of graphene layers deposition by a pyrolytic route are analyzed: the transition had no influence in apparent kinetics, but the carbon structure was totally different. The transition temperature from hybrid to pyrolytic growth varies with the gas pressure: higher temperature transition was possible using lower active gas pressures. The rate-determining step concept is essential to understanding the behavior. In catalytic and hybrid carbon formation, the slower step controls and determines kinetics. In the pyrolytic region, the faster step dominates, and carbon bulk diffusion is blocked: layers of graphene cover the external catalyst surface. It is easier to optimize CNTs growth (rate, shape, properties) knowing the details of the alternative mechanisms operating. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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22 pages, 4599 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Free Radical Photopolymerization and 3D Printing Using Newly Developed Dyes: Indane-1,3-Dione and 1H-Cyclopentanaphthalene-1,3-Dione Derivatives as Photoinitiators in Three-Component Systems

by Ke Sun, Corentin Pigot, Hong Chen, Malek Nechab, Didier Gigmes, Fabrice Morlet-Savary, Bernadette Graff, Shaohui Liu, Pu Xiao, Frédéric Dumur and Jacques Lalevée

Catalysts 2020, 10(4), 463; https://doi.org/10.3390/catal10040463 - 24 Apr 2020

Cited by 41 | Viewed by 4637

Abstract

The design of photoinitiating systems with excellent photochemical reactivities at 405nm LED is one of the obstacles to efficiently promote free radical polymerization in mild conditions (e.g., low light intensity, under air). Here, our actual search for new multicomponent photoinitiating systems at 405nm [...] Read more.

The design of photoinitiating systems with excellent photochemical reactivities at 405nm LED is one of the obstacles to efficiently promote free radical polymerization in mild conditions (e.g., low light intensity, under air). Here, our actual search for new multicomponent photoinitiating systems at 405nm LED prompts us to develop new dyes based on push–pull structures. In the present paper, we chose two series of new dyes which possess indane-1,3-dione and 1H-cyclopenta naphthalene-1,3-dione groups as the electron-withdrawing groups, since they have the great potential to behave as sensitive and remarkable photoinitiators in vat photopolymerization/3D printing. When incorporated with a tertiary amine (ethyl dimethylaminobenzoate EDB, used as electron/hydrogen donor) and an iodonium salt (used as electron acceptor) as the three-component photoinitiating systems (PISs), and among a series of 21 dyes, 10 of them could efficiently promote the free radical photopolymerization of acrylates. Interestingly, steady state photolysis experiments revealed different behaviors of the dyes. Fluorescence experiments and free energy change calculations for redox processes were also carried out to investigate the relevant chemical mechanisms. Additionally, the formation of radicals from the investigated PISs was clearly observed by electron spin resonance (ESR) spin-trapping experiments. Finally, stereoscopic 3D patterns were successfully fabricated by the laser writing technique. In this work, the use of push–pull dyes based on the naphthalene scaffold as photoinitiators of polymerization is reported for the first time in a systematic study aiming at investigating the structure–performance relationship for irradiation carried out at 405 nm. By carefully selecting the electron donors used in the two series of push–pull dyes, novel and high-performance photoinitiating systems operating at 405 nm are thus proposed. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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23 pages, 6194 KiB

Open AccessArticle

Bimetallic Pd-Au/SiO₂ Catalysts for Reduction of Furfural in Water

by Magdalena Modelska, Michal J. Binczarski, Zbigniew Kaminski, Stanislaw Karski, Beata Kolesinska, Pawel Mierczynski, Courtney J. Severino, Andrei Stanishevsky and Izabela A. Witonska

Catalysts 2020, 10(4), 444; https://doi.org/10.3390/catal10040444 - 20 Apr 2020

Cited by 20 | Viewed by 5036

Abstract

Catalytic systems based on bimetallic Pd-Au particles deposited on SiO₂ were prepared by ultrasonically assisted water impregnation and used in the hydrogenation of furfural obtained by the acidic hydrolysis of waste biomass (brewery’s spent grain) in aqueous phase. Pd-Au/SiO₂ catalysts containing [...] Read more.

Catalytic systems based on bimetallic Pd-Au particles deposited on SiO₂ were prepared by ultrasonically assisted water impregnation and used in the hydrogenation of furfural obtained by the acidic hydrolysis of waste biomass (brewery’s spent grain) in aqueous phase. Pd-Au/SiO₂ catalysts containing 50 g of Pd and 2–100 g of Au per 1 kg of catalyst were characterized by high activity in the studied process and, depending on the Pd/Au ratio, selectivity to 2-methyloxolan-2-ol. The modification of 5%Pd/SiO₂ by Au leads to the formation of dispersed Au-Pd solid solution phases, which was confirmed by XRD, XPS, ToF-SIMS, SEM-EDS, and H₂-TPR techniques. The effect of dilution of surface palladium by gold atoms is probably crucial for modification of the reaction mechanism and formation of 2-methyloxolan-2-ol as the main product. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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15 pages, 2709 KiB

Open AccessArticle

Dynamic and Steady State Evolution of Active Sites in H-ZSM5

by Khalid A. Al-Majnouni, Wojciech Supronowicz, Talal Aldugman, Nabil Al-Yassir, Ahmed Al-Zenaidi, Jens Nagengast and Thomas Matuszyk

Catalysts 2020, 10(4), 425; https://doi.org/10.3390/catal10040425 - 13 Apr 2020

Cited by 1 | Viewed by 2685

Abstract

Catalytic cracking of hexane over steamed ZSM-5 is studied under steady state and dynamic conditions to elucidate the role of the active sites on the product distribution. The product distribution from the riser simulator representing the dynamic state of the catalyst cannot be [...] Read more.

Catalytic cracking of hexane over steamed ZSM-5 is studied under steady state and dynamic conditions to elucidate the role of the active sites on the product distribution. The product distribution from the riser simulator representing the dynamic state of the catalyst cannot be resembled from monocracking or bimolecular reactions by Bronsted acid sites alone. The catalyst promotes the hydride transfer function which controls the hexane conversion at 460–500 °C that flips into methanation function at 550 °C with a propene to ethene ratio of 1.04. In addition, hydrogen induction is observed in the first two pulses. Steady state data obtained from a fixed bed reactor, on the other side, shows that the product distribution is controlled by monomolecular cracking with low yield of methane and high propene to ethene ratio ranging from 4.3 to 3.3 depending on the temperature and conversion. We are not able to explain these data by considering the Bronsted acid sites alone and suggest that Lewis acid sites with short-lived activity are not inactive in the carbon-carbon activation before fading by coke deactivation. The reported findings are of importance to academia and industry and are very relevant to fluid catalytic cracking (FCC) processes. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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11 pages, 4597 KiB

Open AccessArticle

Novel Low Temperature Route to Produce CdS/ZnO Composite Nanofibers as Effective Photocatalysts

by Abdullah M. Al-Enizi, M. M. El-Halwany, Mohammed A. Al-Abdrabalnabi, Mahmoud Bakrey, Mohd Ubaidullah and Ayman Yousef

Catalysts 2020, 10(4), 417; https://doi.org/10.3390/catal10040417 - 10 Apr 2020

Cited by 18 | Viewed by 2703

Abstract

In this work, CdS/ZnO composite nanofibers (NFs) were prepared by the electrospinning of a sol–gel comprised of poly(caprolactone), zinc acetate dihydrate, cadmium acetate dihydrate, and ammonium sulfide. The electrospun NF mats were calcined under vacuum in an argon (Ar) atmosphere at 200 °C [...] Read more.

In this work, CdS/ZnO composite nanofibers (NFs) were prepared by the electrospinning of a sol–gel comprised of poly(caprolactone), zinc acetate dihydrate, cadmium acetate dihydrate, and ammonium sulfide. The electrospun NF mats were calcined under vacuum in an argon (Ar) atmosphere at 200 °C for 1 h. Standard physiochemical analysis techniques demonstrated the formation of the crystalline hexagonal phase of CdS and ZnO. Composite NFs showed good photocatalytic degradation of methylene blue (MB) dye under visible light irradiation compared to their counterparts. CdS nanoparticles, ZnO nanofibers, and composite NFs photodegraded 35.5%, 47.3%, and 90% of the MB dye, respectively, within 100 min. The reaction kinetics of MB photodegradation using the composite NFs followed the pseudo-first-order relation. Owing to their facile preparation and good photodegradation ability, the proposed method can be used to prepare various photocatalysts for wastewater treatment. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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15 pages, 7453 KiB

Open AccessArticle

The Impact of In Situ Polymerization Conditions on the Structures and Properties of PANI/ZnO-Based Multiphase Composite Photocatalysts

by Vanja Gilja, Ivana Živković, Teodoro Klaser, Željko Skoko, Marijana Kraljić Roković, Zlata Hrnjak-Murgić and Mark Žic

Catalysts 2020, 10(4), 400; https://doi.org/10.3390/catal10040400 - 5 Apr 2020

Cited by 13 | Viewed by 3234

Abstract

We have synthesized polyaniline/ZnO-based (PANI/ZnO) multiphase composite photocatalysts from acid media by a newly proposed two-step in situ polymerization. The first step of synthesis yielded PANI salt required for the PANI/ZnO synergistic effect. In the second step, the aniline oxidation continued, without ZnO [...] Read more.

We have synthesized polyaniline/ZnO-based (PANI/ZnO) multiphase composite photocatalysts from acid media by a newly proposed two-step in situ polymerization. The first step of synthesis yielded PANI salt required for the PANI/ZnO synergistic effect. In the second step, the aniline oxidation continued, without ZnO dissolution, and it produced PANI base. Thus, both PANI salt and base phases in the composites were detected by FTIR and UV/Vis, while the presence of both ZnO and PANI polymer was confirmed by XRD. Additionally, XRD also showed Zn₅(OH)₈(NO₃)₂·2H₂O and Zn(SO₄)(H₂O) phases in PANI/ZnO-based multiphase composites. Furthermore, the impact of the synthesis conditions on the morphology of the composites was investigated by FE-SEM. The images displayed that ZnO particles were encapsulated in PANI sheets that were formed by the aniline oligomers. Photocatalytic evaluation of PANI/ZnO-based catalysts (i.e., degradation of Acid Blue 25 dye) was conducted and the obtained results confirmed that all the studied composites experienced the PANI/ZnO synergistic effect. It was observed that the best photocatalytic properties were held by the PANI/ZnO_2 sample due to its optimal particle size. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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17 pages, 3127 KiB

Open AccessArticle

LaCO₃OH Nanoprisms and Their Luminescence and NO Reduction Properties

by Md. Hasan Zahir, Mohammad Mominur Rahman, Md Shafiullah, Mohammad Mizanur Rahman, Amjad Ali, Firoz Khan, Khaled Own Mohaisen and Masoud Al-Rasheidi

Catalysts 2020, 10(4), 394; https://doi.org/10.3390/catal10040394 - 3 Apr 2020

Cited by 3 | Viewed by 3186

Abstract

In this work, single-crystalline large-scale LaCO₃OH nanoprism morphologies were synthesized by controlling La and Ca molar ratio and the hydrothermal reaction conditions. The nanoprism morphologies of LaCO₃OH were unique in nature with a sharp corner and smooth surfaces. The [...] Read more.

In this work, single-crystalline large-scale LaCO₃OH nanoprism morphologies were synthesized by controlling La and Ca molar ratio and the hydrothermal reaction conditions. The nanoprism morphologies of LaCO₃OH were unique in nature with a sharp corner and smooth surfaces. The hydrothermal reaction was carried out in the absence of organic additives or templates and (NH₄)₂CO₃ was used as a precipitation agent. The molar ratio of La:Ca was varied over the following values (the sample shorthand is given in parentheses): 75:25 mol% (LC-1), 50:50 mol% (LC-2), and 25:75 mol% (LC-3). Phase-pure LaCO₃OH nanoprisms formed at a La:Ca molar ratio of 75:25 mol% without any assistance of catalysts or template. The photoluminescence (PL) properties of the as-synthesized powders showed one broad emission band centered at 394 nm after excitation of the pure LC-3 LaCO₃OH nanoprisms at λ = 280 nm. The PL intensities were decreased in the order of LC-1 < LC-2< LC-3. The LC-1 and LC-2 samples had almost the same PL intensities probably due to their unique and smooth particle morphology. The calcination result of three samples treated for two hours at 800 °C, shows a reduction in NO activities over highly distributed CaO comprising La₂O₃. Further, under the presence of H₂O and O₂ vapor_, CaO comprising La₂O₃ catalysts shows higher stability for the reduction of NO with CH₄. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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13 pages, 3151 KiB

Open AccessArticle

Study on Thermal Decomposition Behavior, Gaseous Products, and Kinetic Analysis of Bis-(Dimethylglyoximato) Nickel(II) Complex Using TG-DSC-FTIR-MS Technique

by Ergang Yao, Siyu Xu, Fengqi Zhao, Taizhong Huang, Haijian Li, Ningning Zhao, Jianhua Yi, Yanjing Yang and Changjian Wang

Catalysts 2020, 10(3), 331; https://doi.org/10.3390/catal10030331 - 15 Mar 2020

Cited by 12 | Viewed by 6115

Abstract

The fiber-like bis-(dimethylglyoximato) nickel(II) complex, Ni(DMG)₂ was successfully synthesized. The obtained samples were characterized by SEM-EDS, FT-IR, XRD, and XPS. The TG-DSC-FTIR-MS coupling technique was used to characterize the thermal decomposition behavior and evolved gas analysis of Ni(DMG)₂. The non-isothermal [...] Read more.

The fiber-like bis-(dimethylglyoximato) nickel(II) complex, Ni(DMG)₂ was successfully synthesized. The obtained samples were characterized by SEM-EDS, FT-IR, XRD, and XPS. The TG-DSC-FTIR-MS coupling technique was used to characterize the thermal decomposition behavior and evolved gas analysis of Ni(DMG)₂. The non-isothermal decomposition reaction kinetic parameters were obtained by both combined kinetic analysis and isoconversional Vyazovkin methods. It was found that Ni(DMG)₂ begins to decompose at around 280 °C, and a sharp exothermic peak is observed in the DSC curve at about 308.2 °C at a heating rate of 10 °C·min⁻¹. The main gaseous products are H₂O, NH₃, N₂O, CO, and HCN, and the content of H₂O is significantly higher than that of the others. The activation energy obtained by the combined kinetic analysis method is 170.61 ± 0.65 kJ·mol⁻¹. The decomposition process can be described by the random nucleation and growth of the nuclei model. However, it was challenging to attempt to evaluate the reaction mechanism precisely by one ideal kinetic model. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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17 pages, 3932 KiB

Open AccessArticle

Ru-Promoted Ni/Al₂O₃ Fluidized Catalyst for Biomass Gasification

by Alan Rubén Calzada Hernandez, Daniel Gibran González Castañeda, Adriana Sánchez Enriquez, Hugo de Lasa and Benito Serrano Rosales

Catalysts 2020, 10(3), 316; https://doi.org/10.3390/catal10030316 - 10 Mar 2020

Cited by 15 | Viewed by 3635

Abstract

Fluidizable catalysts based on Ni/Al₂O₃ with added Ru were used for the gasification of a lignin surrogate (2-methoxy-4-methylphenol) in a fluidized CREC Riser Simulator reactor. This was done in order to quantify lignin surrogate conversion and lignin surrogate products (H [...] Read more.

Fluidizable catalysts based on Ni/Al₂O₃ with added Ru were used for the gasification of a lignin surrogate (2-methoxy-4-methylphenol) in a fluidized CREC Riser Simulator reactor. This was done in order to quantify lignin surrogate conversion and lignin surrogate products (H₂, CO, CO₂ and CH₄) as well as the coke deposited on the catalyst. The catalysts that were evaluated contained 5% wt. Ni with various Ru loadings (0.25%, 0.5% and 1% wt). These catalysts were synthesized using an incipient Ni and Ru co-impregnation. Catalysts were characterized using XRD, N₂adsorption-desorption (BET Surface Area, BJH), Temperature Programmed Reduction (TPR), Temperature Programmed Desorption (TPD) and H₂ chemisorption. Catalytic steam gasification took place at 550, 600 and 650 °C using 0.5, 1.0 and 1.5, steam/biomass ratios. The results obtained showed that Ru addition helped to decrease both nickel crystallite site sizes and catalyst acid site density. Moreover, it was observed that coke on the catalyst was reduced by 60%. This was the case when compared to the runs with the Ni/Al₂O₃ free of Ru. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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14 pages, 3203 KiB

Open AccessArticle

Nitric Acid Functionalization of Petroleum Coke to Access Inherent Sulfur

by Qing Huang, Annelisa S. Schafranski, Melanie J. Hazlett, Ye Xiao and Josephine M. Hill

Catalysts 2020, 10(2), 259; https://doi.org/10.3390/catal10020259 - 20 Feb 2020

Cited by 16 | Viewed by 6246

Abstract

Sulfonated carbon-based catalysts have been identified as promising solid acid catalysts, and petroleum coke (petcoke), a byproduct of the oil industry, is a potential feedstock for these catalysts. In this study, sulfur-containing (6.5 wt%) petcoke was used as a precursor for these catalysts [...] Read more.

Sulfonated carbon-based catalysts have been identified as promising solid acid catalysts, and petroleum coke (petcoke), a byproduct of the oil industry, is a potential feedstock for these catalysts. In this study, sulfur-containing (6.5 wt%) petcoke was used as a precursor for these catalysts through direct functionalization (i.e., without an activation step) with nitric acid to access the inherent sulfur. Catalysts were also prepared using sulfuric acid and a mixture of nitric and sulfuric acid (1:3 vol ratio). Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and titration were used to identify and quantify the acid sites. The activities of the prepared catalysts were determined for the esterification of octanoic acid with methanol. Petcoke had few −SO₃H groups, and correspondingly no catalytic activity for the reaction. All acid treatments increased the number of −SO₃H groups and promoted esterification. Treatment with nitric acid alone resulted in the oxidation of the inherent sulfur in petcoke to produce ~0.7 mmol/g of strong acid sites and a total acidity of 5.3 mmol/g. The acidity (strong acid and total) was lower with sulfuric acid treatment but this sample was more active for the esterification reaction (TOF of 31 h⁻¹ compared to 7 h⁻¹ with nitric acid treatment). Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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18 pages, 4092 KiB

Open AccessArticle

Enhanced Visible Light Photocatalytic Activity of N and Ag Doped and Co-Doped TiO₂ Synthesized by Using an In-Situ Solvothermal Method for Gas Phase Ammonia Removal

by Adilah Sirivallop, Thanita Areerob and Siriluk Chiarakorn

Catalysts 2020, 10(2), 251; https://doi.org/10.3390/catal10020251 - 19 Feb 2020

Cited by 56 | Viewed by 6727

Abstract

Single doping and co-doping of N and Ag on TiO₂ were successfully prepared by using an in-situ solvothermal method and their structural properties and chemical compositions were characterized. The results indicated that all photocatalysts displayed in TiO₂ anatase crystal phase, and [...] Read more.

Single doping and co-doping of N and Ag on TiO₂ were successfully prepared by using an in-situ solvothermal method and their structural properties and chemical compositions were characterized. The results indicated that all photocatalysts displayed in TiO₂ anatase crystal phase, and a small mesoporous structure was observed in the doped materials. The main roles of N and Ag on the property and photocatalytic activity of TiO₂ were different. The N doping has significantly enhanced homogenous surface morphology and specific surface area of the photocatalyst. While Ag doping was narrowing the band gap energy, extending light absorption toward a visible region by surface plasmon resonance as well as delaying the recombination rate of electron and hole of TiO₂. The existence of N in TiO₂ lattice was observed in two structural linkages such as substitutional nitrogen (Ti-O-N) and interstitial nitrogen (O-Ti-N). Silver species could be in the form of Ag⁰ and Ag₂O. The photocatalytic performance of the photocatalysts coated on stainless steel mesh was investigated by the degradation of aqueous MB and gas phase NH₃ under visible LED light illumination for three recycling runs. The highest photocatalytic activity and recyclability were reached in 5% N/Ag-TiO₂ showing the efficiency of 98.82% for methylene blue (MB) dye degradation and 37.5% for NH₃ removal in 6 h, which was 2.7 and 4.3 times, respectively. This is greater than that of pure TiO₂. This was due to the synergistic effect of N and Ag doping. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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14 pages, 3307 KiB

Open AccessArticle

The Influence of The Light-Activated Titania P25 on Human Breast Cancer Cells

by Agata Markowska-Szczupak, Zhishun Wei and Ewa Kowalska

Catalysts 2020, 10(2), 238; https://doi.org/10.3390/catal10020238 - 17 Feb 2020

Cited by 6 | Viewed by 3656

Abstract

Cosmetics and other daily care products contain titanium(IV) oxide (titania). Since multiple risk factors can increase the chance of developing cancer, an evaluation of titania safety has become a matter of concern in recent times. However, it should be pointed out that titania [...] Read more.

Cosmetics and other daily care products contain titanium(IV) oxide (titania). Since multiple risk factors can increase the chance of developing cancer, an evaluation of titania safety has become a matter of concern in recent times. However, it should be pointed out that titania as an efficient photocatalyst has been also applied for inactivation of various pathogens, environmental purification and energy conversion, which might result in significant improvement of human life. Therefore, it is worth considering titania not only as a possible cancer initiator, but also as an efficient solution against cancer cells. Accordingly, in this study, the effect of commercial titania photocatalyst P25 (Degussa/Evonik) on breast adenocarcinoma MCF7 cells (ATCC^® HTB-22™, breast adenocarcinoma cell line from human) has been investigated. The cells were treated with titania at doses of 10, 30, and 50 µg/mL under UVA/vis irradiation and in the dark. The significant morphological alterations in living cells were observed for larger doses of titania, such as changes in the shape and the size of cells, the deviation from the normal structure, and an increase in cells’ mortality. Moreover, the effect was significantly higher under irradiation than in the dark confirming strong photocatalytic activity of titania P25. In contrast, the lowest dose of titania (10 µg/mL) did not exhibit a significant impact on MCF7 cells, similarly to the nontreated cells. Accordingly, it has been proposed that locally applied titania might be considered for a cancer therapy after necessary in vivo tests to estimate any possibilities of side effects. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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24 pages, 4898 KiB

Open AccessArticle

Photoreduction of a Pd-Doped Mesoporous TiO₂ Photocatalyst for Hydrogen Production under Visible Light

by Bianca Rusinque, Salvador Escobedo and Hugo de Lasa

Catalysts 2020, 10(1), 74; https://doi.org/10.3390/catal10010074 - 3 Jan 2020

Cited by 34 | Viewed by 6594

Abstract

Photoreduction with visible light can enhance the photocatalytic activity of TiO₂ for the production of hydrogen. In this article, we present a strategy to photoreduce a palladium-doped TiO₂ photocatalyst by using near-UV light prior to its utilization. A sol-gel methodology was [...] Read more.

Photoreduction with visible light can enhance the photocatalytic activity of TiO₂ for the production of hydrogen. In this article, we present a strategy to photoreduce a palladium-doped TiO₂ photocatalyst by using near-UV light prior to its utilization. A sol-gel methodology was employed to prepare the photocatalysts with different metal loadings (0.25–5.00 wt% Pd). The structural and morphological characteristics of the synthesized Pd-TiO₂ were analyzed by using X-ray Diffraction (XRD), BET Surface Area (S_BET), TemperatureProgrammed Reduction (TPR), Chemisorption and X-ray Photoelectron Spectroscopy (XPS). Hydrogen was produced by water splitting under visible light irradiation using ethanol as an organic scavenger. Experiments were developed in the Photo-CREC Water-II (PCW-II) Reactor designed at the CREC-UWO (Chemical Reactor Engineering Centre). It was shown that the mesoporous 0.25 wt% Pd-TiO₂ with 2.5 1eV band gap exhibits, under visible light, the best hydrogen production performance, with a 1.58% Quantum Yield being achieved. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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15 pages, 7465 KiB

Open AccessArticle

Energy-Saving UHMW Polymeric Flow Aids: Catalyst and Polymerization Process Development

by Muhammad Atiqullah, Abdelsalam H. Al-Sarkhi, Faisal M. Al-Thenayan, Abdullah R. Al-Malki and Hassan S. Alasiri

Catalysts 2019, 9(12), 1002; https://doi.org/10.3390/catal9121002 - 28 Nov 2019

Cited by 4 | Viewed by 3554

Abstract

Crude oil and refinery products are transported worldwide to meet human energy needs. During transportation via pipeline, huge pumping power is required to overcome the frictional pressure drop and the associated drag along the pipeline. The reduction of both is of great interest [...] Read more.

Crude oil and refinery products are transported worldwide to meet human energy needs. During transportation via pipeline, huge pumping power is required to overcome the frictional pressure drop and the associated drag along the pipeline. The reduction of both is of great interest to industry and academia. Highly expensive ultrahigh molecular weight (UHMW, MW a million Dalton) drag reducing polymers (DRPs) are currently used to address this problem. The present paper, therefore, emphasizes particularly the development of a high-performance catalyst system that synthesizes DRPs (using higher alpha-olefins)—a highly promising cost reduction alternative. This homogeneous catalyst system features a new concept that uses a cost-effective titanium-based Ziegler–Natta precatalyst and a cocatalystLewis base complex having both steric hindrance (around N heteroatom) and electronic effect. This novel work, which involves precatalyst–cocatalyst molecular separation and cocatalystmonophenyl amine association-dissociation phenomena, already generated several US patents. The subject catalyst prepares UHMW DRPs at room temperature, avoiding the use of zero and sub-zero temperatures. The resulting product almost tripled the rate of transportation of a selected grade of refinery product and saved about 50% pumping energy at ppm level pipeline concentration. It is also very easily soluble. Hence, massive modification of existing pipeline will be unnecessary. This will save additional infrastructure cost. This paper also summarizes challenges facing the development of improved heterogeneous catalysts, dispersed polymerization process, molecular simulation-based DRP product formulation, and model/theory of turbulent mixing and dispersion in the transportation pipeline setting. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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15 pages, 2176 KiB

Open AccessArticle

Synthesis of Fatty Acid Methyl Esters from Pomace Oil Catalyzed by Zinc Stearate: A Kinetic Study of the Transesterification and Esterification Reactions

by Mariana Soledad Alvarez Serafini and Gabriela Marta Tonetto

Catalysts 2019, 9(12), 978; https://doi.org/10.3390/catal9120978 - 21 Nov 2019

Cited by 7 | Viewed by 4357

Abstract

In this work, the simultaneous transesterification and esterification reactions of olive pomace oil with methanol catalyzed by zinc stearate were studied. This catalyst is a crystalline solid at room temperature, but it is soluble in the reaction medium at reaction temperature. Zinc stearate [...] Read more.

In this work, the simultaneous transesterification and esterification reactions of olive pomace oil with methanol catalyzed by zinc stearate were studied. This catalyst is a crystalline solid at room temperature, but it is soluble in the reaction medium at reaction temperature. Zinc stearate has surfactant properties that cause the formation of an emulsion in the reaction system. The stability of the emulsion formed in the oil–methanol–catalyst system was compared to that in the FAME (fatty acid methyl esters)–methanol–catalyst system. It was observed that the emulsion formed in the presence of high amounts of FAME is much more unstable, which makes the catalyst easy to separate from the reaction products. The kinetics of esterification and transesterification were also studied. All the kinetic and equilibrium constants were determined with a complete model, considering the three stepwise reactions corresponding to the transesterification of triglycerides and the esterification of free fatty acids. The parameters obtained were used to model the operating conditions that would allow obtaining biodiesel that meets the quality standards. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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Review

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27 pages, 7345 KiB

Open AccessReview

The Origin of Au/Ce_1-xZr_xO₂ Catalyst’s Active Sites in Low-Temperature CO Oxidation

by Izabela Dobrosz-Gómez, Miguel-Ángel Gómez-García and Jacek Michał Rynkowski

Catalysts 2020, 10(11), 1312; https://doi.org/10.3390/catal10111312 - 13 Nov 2020

Cited by 3 | Viewed by 2543

Abstract

Gold catalysts have found applications in many reactions of both industrial and environmental importance. Great interest has been paid to the development of new processes that reduce energy consumption and minimize pollution. Among these reactions, the catalytic oxidation of carbon monoxide (CO) is [...] Read more.

Gold catalysts have found applications in many reactions of both industrial and environmental importance. Great interest has been paid to the development of new processes that reduce energy consumption and minimize pollution. Among these reactions, the catalytic oxidation of carbon monoxide (CO) is an important one, considering that a high concentration of CO in the atmosphere creates serious health and environmental problems. This paper examines the most important achievements and conclusions arising from the own authorship contributions concerning (2 wt. % Au)/Ce_1−xZr_xO₂ catalyst’s active sites in low-temperature CO oxidation. The main findings of the present review are: (1) The effect of preparing conditions on Au crystallite size, highlighting some of the fundamental underpinnings of gold catalysis: the Au surface composition and the poisoning effect of residual chloride on the catalytic activity of (2 wt. % Au)/Ce_1−xZr_xO₂ catalysts in CO oxidation; (2) The identification of ion clusters related to gold and their effect on catalyst’ surface composition; (3) The importance of physicochemical properties of oxide support (e.g., its particle size, oxygen mobility at low temperature and redox properties) in the creation of catalytic performance of Au catalysts; (4) The importance of oxygen vacancies, on the support surface, as the centers for oxygen molecule activation in CO reaction; (5) The role of moisture (200–1000 ppm) in the generation of enhanced CO conversion; (6) The Au-assisted Mars-van Krevelen (MvK) adsorption–reaction model was pertinent to describe CO oxidation mechanism. The principal role of Au in CO oxidation over (2 wt. % Au)/Ce_1−xZr_xO₂ catalysts was related to the promotion in the transformation process of reversibly adsorbed or inactive surface oxygen into irreversibly adsorbed active species; (7) Combination of metallic gold (Au⁰) and Au-OH species was proposed as active sites for CO adsorption. These findings can help in the optimization of Au-containing catalysts. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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25 pages, 2557 KiB

Open AccessReview

Application of Heterogeneous Catalysts for Biodiesel Production from Microalgal Oil—A Review

by Mohammed O. Faruque, Shaikh A. Razzak and Mohammad M. Hossain

Catalysts 2020, 10(9), 1025; https://doi.org/10.3390/catal10091025 - 7 Sep 2020

Cited by 143 | Viewed by 15067

Abstract

The depletion of fossil fuel reserves and increased environmental concerns related to fossil fuel production and combustion has forced the global communities to search for renewable fuels. In this regard, microalgae-based biodiesel has been considered as one of the interesting alternatives. Biodiesel production [...] Read more.

The depletion of fossil fuel reserves and increased environmental concerns related to fossil fuel production and combustion has forced the global communities to search for renewable fuels. In this regard, microalgae-based biodiesel has been considered as one of the interesting alternatives. Biodiesel production from the cultivation of microalgae is eco-friendly and sustainable. Moreover, microalgae have several advantages over other bioenergy sources, including their good photosynthetic capacity and faster growth rates. The productivity of microalgae per unit land area is also significantly higher than that of terrestrial plants. The produced microalgae biomass is rich with high quality lipids, which can be converted into biodiesel by transesterification reactions. Generally, the transesterification reactions are carried out in the presence of a homogeneous or heterogeneous catalyst. The homogeneous catalysts have many disadvantages, including their single use, slow reaction rate and saponification issues due to the presence of fatty acids in the feedstock. The acidic nature of the homogeneous catalysts also causes equipment corrosion. On the other hand, the heterogeneous catalysts offer several advantages, including their reusability, higher reaction rate and selectivity, easy product/catalyst separation and low cost. Due to these facts, the development of solid phase transesterification catalysts have been receiving growing interest. The present review is focused on the use of heterogeneous catalysts for biodiesel production from microalgal oil as a reliable feedstock with a comparison to other available feedstocks. It also highlights optimal reaction conditions for maximum biodiesel yields, reusability of the solid catalysts, cost, and environmental impact. The superior lipid content of microalgae and the efficient concurrent esterification and transesterification of the solid acid−base catalysts can offer new advancements in biodiesel production. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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38 pages, 7405 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photocatalysis for Air Treatment Processes: Current Technologies and Future Applications for the Removal of Organic Pollutants and Viruses

by Salvador Escobedo and Hugo de Lasa

Catalysts 2020, 10(9), 966; https://doi.org/10.3390/catal10090966 - 24 Aug 2020

Cited by 32 | Viewed by 9118

Abstract

Photocatalysis for air treatment or photocatalytic oxidation (PCO) is a relatively new technology which requires titanium dioxide (TiO₂) and a source of light (Visible or near-UV) to degrade pollutants contained in air streams. Present approaches for the photodegradation of indoor pollutants [...] Read more.

Photocatalysis for air treatment or photocatalytic oxidation (PCO) is a relatively new technology which requires titanium dioxide (TiO₂) and a source of light (Visible or near-UV) to degrade pollutants contained in air streams. Present approaches for the photodegradation of indoor pollutants in air streams aim to eliminate volatile organic compounds (VOCs) and viruses, which are both toxic and harmful to human health. Photocatalysis for air treatment is an inexpensive and innovative green process. Additionally, it is a technology with a reduced environmental footprint when compared to other conventional air treatments which demand significant energy, require the disposal of used materials, and release CO₂ and other greenhouse gases to the environment. This review discusses the most current and relevant information on photocatalysis for air treatment. This article also provides a critical review of (1) the most commonly used TiO₂-based semiconductors, (2) the experimental syntheses and the various photocatalytic organic species degradation conversions, (3) the developed kinetics and computational fluid dynamics (CFD) and (4) the proposed Quantum Yields (QYs) and Photocatalytic Thermodynamic Efficiency Factors (PTEFs). Furthermore, this article contains important information on significant factors affecting the photocatalytic degradation of organic pollutants, such as reactor designs and type of photoreactor irradiation. Overall, this review describes state-of-the-art photocatalysis for air treatment to eliminate harmful indoor organic molecules, reviewing as well the potential applications for the inactivation of SARS-CoV2 (COVID-19) viruses. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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24 pages, 3427 KiB

Open AccessFeature PaperReview

Propane Oxidative Dehydrogenation on Vanadium-Based Catalysts under Oxygen-Free Atmospheres

by Samira Rostom and Hugo de Lasa

Catalysts 2020, 10(4), 418; https://doi.org/10.3390/catal10040418 - 10 Apr 2020

Cited by 27 | Viewed by 6981

Abstract

Catalytic propane oxidative dehydrogenation (PODH) in the absence of gas phase oxygen is a promising approach for propylene manufacturing. PODH can overcome the issues of over-oxidation, which lower propylene selectivity. PODH has a reduced environmental footprint when compared with conventional oxidative dehydrogenation, which [...] Read more.

Catalytic propane oxidative dehydrogenation (PODH) in the absence of gas phase oxygen is a promising approach for propylene manufacturing. PODH can overcome the issues of over-oxidation, which lower propylene selectivity. PODH has a reduced environmental footprint when compared with conventional oxidative dehydrogenation, which uses molecular oxygen and/or carbon dioxide. This review discusses both the stoichiometry and the thermodynamics of PODH under both oxygen-rich and oxygen-free atmospheres. This article provides a critical review of the promising PODH approach, while also considering vanadium-based catalysts, with lattice oxygen being the only oxygen source. Furthermore, this critical review focuses on the advances that were made in the 2010–2018 period, while considering vanadium-based catalysts, their reaction mechanisms and performances and their postulated kinetics. The resulting kinetic parameters at selected PODH conditions are also addressed. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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17 pages, 825 KiB

Open AccessReview

SiO₂@TiO₂ Composite Synthesis and Its Hydrophobic Applications: A Review

by Alicia Rosales and Karen Esquivel

Catalysts 2020, 10(2), 171; https://doi.org/10.3390/catal10020171 - 2 Feb 2020

Cited by 48 | Viewed by 15348

Abstract

Titanium dioxide is well known for its photocatalytic properties and low toxicity, meanwhile, silicone dioxide exhibits hydrophobic and hydrophilic properties and thermal stability. The union of these two materials offers a composite material with a wide range of applications that relate directly to [...] Read more.

Titanium dioxide is well known for its photocatalytic properties and low toxicity, meanwhile, silicone dioxide exhibits hydrophobic and hydrophilic properties and thermal stability. The union of these two materials offers a composite material with a wide range of applications that relate directly to the combined properties. The SiO₂-TiO₂ composite has been synthesized through physical methods and chemical methods and, with adequate conditions, morphology, crystallinity, boundaries between SiO₂-TiO₂, among other properties, can be controlled. Thus, the applications of this composite are wide for surface applications, being primarily used as powder or coating. However, the available research information on this kind of composite material is still novel, therefore research in this field is still needed in order to clarify all the physical and chemical properties of the material. This review aims to encompass the available methods of synthesis of SiO₂-TiO₂ composite with modifiers or dopants, the application and known chemical and physical properties in surfaces such as glass, mortar and textile, including aspects for the development of this material. Full article

(This article belongs to the Special Issue Commemorative Issue in Honor of Professor Hugo de Lasa)

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