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19 pages, 3132 KiB

Open AccessArticle

Synthesis and Evaluation of Copper-Supported Titanium Oxide Nanotubes as Electrocatalyst for the Electrochemical Reduction of Carbon Oxide to Organics

by SK Safdar Hossain, Junaid Saleem, SleemUr Rahman, Syed Mohammed Javaid Zaidi, Gordon McKay and Chin Kui Cheng

Catalysts 2019, 9(3), 298; https://doi.org/10.3390/catal9030298 - 25 Mar 2019

Cited by 27 | Viewed by 5540

Abstract

Carbon dioxide (CO₂) is considered as the prime reason for the global warming effect and one of the useful ways to transform it into an array of valuable products is through electrochemical reduction of CO₂ (ERC). This process requires an [...] Read more.

Carbon dioxide (CO₂) is considered as the prime reason for the global warming effect and one of the useful ways to transform it into an array of valuable products is through electrochemical reduction of CO₂ (ERC). This process requires an efficient electrocatalyst with high faradaic efficiency at low overpotential and enhanced reaction rate. Herein, we report an innovative way of reducing CO₂ using copper-metal supported on titanium oxide nanotubes (TNT) electrocatalysts. The TNT support material was synthesized using alkaline hydrothermal process with Degussa (P-25) as a starting material. Copper nanoparticles were anchored on the TNT by homogeneous deposition-precipitation method (HDP) with urea as precipitating agent. The prepared catalysts were tested in a home-made H-cell with 0.5 M NaHCO₃ aqueous solution in order to examine their activity for ERC and the optimum copper loading. Continuous gas-phase ERC was carried out in a solid polymer electrolyte (SPE) reactor. The 10% Cu/TNT catalysts were employed in the gas diffusion layer (GDL) on the cathode side with Pt-Ru/C on the anode side. Faradaic efficiencies for the three major products namely methanol, methane, and CO were found to be 4%, 3%, and 10%, respectively at −2.5 V with an overall current density of 120 mA/cm². The addition of TNT significantly increased the catalytic activity of electrocatalyst for ERC. It is mainly attributed to their better stability towards oxidation, increased CO₂ adsorption capacity and stabilization of the reaction intermediate, layered titanates, and larger surface area (400 m²/g) as compared with other support materials. Considering the low cost of TNT, it is anticipated that TNT support electrocatalyst for ECR will gain popularity. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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22 pages, 12840 KiB

Open AccessArticle

Photocatalytic Activity of Nanostructured Titania Films Obtained by Electrochemical, Chemical, and Thermal Oxidation of Ti6Al4V Alloy—Comparative Analysis

by Aleksandra Radtke

Catalysts 2019, 9(3), 279; https://doi.org/10.3390/catal9030279 - 19 Mar 2019

Cited by 3 | Viewed by 3921

Abstract

Three different Ti6Al4V surface oxidation methods have been applied to obtain three types of titania materials of different nanoarchitecture. Electrochemical oxidation of titanium alloy allowed for obtaining titania nanotubes (TNT), chemical oxidation led to obtain titania nanofibers (TNF), and thermal oxidation gave titania [...] Read more.

Three different Ti6Al4V surface oxidation methods have been applied to obtain three types of titania materials of different nanoarchitecture. Electrochemical oxidation of titanium alloy allowed for obtaining titania nanotubes (TNT), chemical oxidation led to obtain titania nanofibers (TNF), and thermal oxidation gave titania nanowires (TNW). My earlier investigations of these nanomaterials were focused mainly on the estimation of their bioactivity and potential application in modern implantology. In this article, the comparative analysis of the photocatalytic activity of produced systems, as well as the impact of their structure and morphology on this activity, are discussed. The activity of studied nanomaterials was estimated basis of UV-induced degradation of methylene blue and also acetone, and it was determined quantitatively according to the Langmuir–Hinshelwood reaction mechanism. The obtained results were compared to the activity of Pilkington Glass Activ^TM (reference sample). Among analyzed systems, titania nanofibers obtained at 140 and 120 °C, possessing anatase and anatase/amorphous structure, as well as titania nanowires obtained at 475 and 500 °C, possessing anatase and anatase/rutile structure, were better photocatalyst than the reference sample. Completely amorphous titania nanotubes, turned out to be an interesting alternative for photocatalytic materials in the form of thin films, however, their photocatalytic activity is lower than for Pilkington Glass Activ^TM. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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17 pages, 45260 KiB

Open AccessArticle

Catalytic Behaviour of Flame-Made CuO-CeO₂ Nanocatalysts in Efficient CO Oxidation

by Feng Zhao, Shuangde Li, Xiaofeng Wu, Renliang Yue, Weiman Li, Xicuo Zha, Yuzhou Deng and Yunfa Chen

Catalysts 2019, 9(3), 256; https://doi.org/10.3390/catal9030256 - 13 Mar 2019

Cited by 33 | Viewed by 4681

Abstract

CuO-CeO₂ nanocatalysts with varying CuO contents (1, 5, 9, 14 and 17 wt %) were prepared by one-step flame spray pyrolysis (FSP) and applied to CO oxidation. The influences of CuO content on the as-prepared catalysts were systematically characterized by X-ray diffraction [...] Read more.

CuO-CeO₂ nanocatalysts with varying CuO contents (1, 5, 9, 14 and 17 wt %) were prepared by one-step flame spray pyrolysis (FSP) and applied to CO oxidation. The influences of CuO content on the as-prepared catalysts were systematically characterized by X-ray diffraction (XRD), N₂ adsorption-desorption at −196 °C, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen-temperature programmed reduction (H₂-TPR). A superior CO oxidation activity was observed for the 14 wt % CuO-CeO₂ catalyst, with 90% CO conversion at 98 °C at space velocity (60,000 mL × g⁻¹ × h⁻¹), which was attributed to abundant surface defects (lattice distortion, Ce³⁺, and oxygen vacancies) and high reducibility supported by strong synergistic interaction. In addition, the catalyst also displayed excellent stability and resistance to water vapor. Significantly, in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) showed that in the CO catalytic oxidation process, the strong synergistic interaction led readily to dehydroxylation and CO adsorption on Cu⁺ at low temperature. Furthermore, in the feed of water vapor, although there was an adverse effect on the access of CO adsorption, there was also a positive effect on the formation of fewer carbon intermediates. All these results showed the potential of highly active and water vapor-resistive CuO-CeO₂ catalysts prepared by FSP. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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15 pages, 2317 KiB

Open AccessArticle

Appraisal of Sulphonation Processes to Synthesize Palm Waste Biochar Catalysts for the Esterification of Palm Fatty Acid Distillate

by Shehu-Ibrahim Akinfalabi, Umer Rashid, Robiah Yunus and Yun Hin Taufiq-Yap

Catalysts 2019, 9(2), 184; https://doi.org/10.3390/catal9020184 - 15 Feb 2019

Cited by 17 | Viewed by 4338

Abstract

Palm waste biochar (PWB) catalysts were synthesized as bio-based catalysts using different sulphonation methods. (NH₄)₂SO₄, ClSO₃H, and H₂SO₄ were applied to functionalize PWB and appraise the discrepancies between the sulfonic agents, as [...] Read more.

Palm waste biochar (PWB) catalysts were synthesized as bio-based catalysts using different sulphonation methods. (NH₄)₂SO₄, ClSO₃H, and H₂SO₄ were applied to functionalize PWB and appraise the discrepancies between the sulfonic agents, as they affect the esterification reaction in terms of fatty acid methyl ester (FAME) yield and conversion while using palm fatty acid distillate (PFAD) as feedstock. The PWB was first soaked in phosphoric acid (H₃PO₄) for 24 h and then pyrolized at 400 °C for 2 h in tube furnace. Afterwards, sulphonation was done with different sulfonic agents and characterized with thermo-gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and temperature programmed desorption–ammonia (TPD-NH₃). The three synthesized catalysts showed high free fatty acid (FFA) conversions of 90.1% for palm waste biochar-ammonium sulfate (PWB-(NH₄)₂SO₄), 91.5% for palm waste biochar-chlorosulfonic acid (PWB-ClSO₃H), and 97.4% for palm waste biochar - sulphuric acid (PWB-H₂SO₄), whereas FAME yields were 88.6% (PWB-(NH₄)₂SO₄), 89.1% (PWB-ClSO₃H), and 96.1% (PWB-H₂SO₄). It was observed that PWB-H₂SO₄ has the best catalytic activity, which was directly linked to its high acid density (11.35 mmol/g), improved pore diameter (6.25 nm), and increased specific surface area (372.01 m² g⁻¹). PWB-H₂SO₄ was used for the reusability study, where it underwent eight reaction runs and was stable until the seventh run. PWB-H₂SO₄ has shown huge promise for biodiesel synthesis, owing to its easy synthetic process, recyclability, and high catalytic activity for waste oils and fats. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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17 pages, 5367 KiB

Open AccessArticle

Ti-Doped Pd-Au Catalysts for One-Pot Hydrogenation and Ring Opening of Furfural

by Nandan Shreehari Date, Valeria La Parola, Chandrashekhar Vasant Rode and Maria Luisa Testa

Catalysts 2018, 8(6), 252; https://doi.org/10.3390/catal8060252 - 20 Jun 2018

Cited by 20 | Viewed by 4538

Abstract

Pd-Au bimetallic catalysts with different Pd/Au atomic ratios, supported on ordered structured silica (Hexagonal mesoporous silica—HMS, or Santa Barbara Amorphous-15—SBA-15) were evaluated for one-pot hydrogenation of furfural to 1,2-pentanediol. The surface and structural properties of the catalysts were deeply investigated by X-ray photoelectron [...] Read more.

Pd-Au bimetallic catalysts with different Pd/Au atomic ratios, supported on ordered structured silica (Hexagonal mesoporous silica—HMS, or Santa Barbara Amorphous-15—SBA-15) were evaluated for one-pot hydrogenation of furfural to 1,2-pentanediol. The surface and structural properties of the catalysts were deeply investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), N₂ adsorption isotherms (BET), Infrared spectroscopy (IR), and acid capacity measurements. XPS studies revealed that Ti doped supports had higher dispersion of the active phase, particularly in the case of Pd-Au materials in which Ti played an important role in stabilizing the metallic species. Among the various process conditions studied, such as temperature (160 °C), catalyst amount (10% w/w), and reaction time (5 h), H₂ pressure (500 psi) was found to improve the 1,2-pentanediol selectivity. The SBA silica bimetallic Ti-doped system showed the best performance in terms of stability and reusability, after multiple cycles. Under specific reaction conditions, the synergism between Pd-Au alloy and Ti doping of the support allowed the ring opening pathway towards the formation of 1,2-pentanediol in furfural hydrogenation. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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Review

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32 pages, 13294 KiB

Open AccessEditor’s ChoiceReview

Mechanistic Insights into Photodegradation of Organic Dyes Using Heterostructure Photocatalysts

by Yi-Hsuan Chiu, Tso-Fu Mark Chang, Chun-Yi Chen, Masato Sone and Yung-Jung Hsu

Catalysts 2019, 9(5), 430; https://doi.org/10.3390/catal9050430 - 9 May 2019

Cited by 609 | Viewed by 21522

Abstract

Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various [...] Read more.

Due to its low cost, environmentally friendly process, and lack of secondary contamination, the photodegradation of dyes is regarded as a promising technology for industrial wastewater treatment. This technology demonstrates the light-enhanced generation of charge carriers and reactive radicals that non-selectively degrade various organic dyes into water, CO₂, and other organic compounds via direct photodegradation or a sensitization-mediated degradation process. The overall efficiency of the photocatalysis system is closely dependent upon operational parameters that govern the adsorption and photodegradation of dye molecules, including the initial dye concentration, pH of the solution, temperature of the reaction medium, and light intensity. Additionally, the charge-carrier properties of the photocatalyst strongly affect the generation of reactive species in the heterogeneous photodegradation and thereby dictate the photodegradation efficiency. Herein, this comprehensive review discusses the pseudo kinetics and mechanisms of the photodegradation reactions. The operational factors affecting the photodegradation of either cationic or anionic dye molecules, as well as the charge-carrier properties of the photocatalyst, are also fully explored. By further analyzing past works to clarify key active species for photodegradation reactions and optimal conditions, this review provides helpful guidelines that can be applied to foster the development of efficient photodegradation systems. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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30 pages, 11140 KiB

Open AccessEditor’s ChoiceReview

Hybrid Catalysts for CO₂ Conversion into Cyclic Carbonates

by Carla Calabrese, Francesco Giacalone and Carmela Aprile

Catalysts 2019, 9(4), 325; https://doi.org/10.3390/catal9040325 - 2 Apr 2019

Cited by 81 | Viewed by 12553

Abstract

The conversion of carbon dioxide into valuable chemicals such as cyclic carbonates is an appealing topic for the scientific community due to the possibility of valorizing waste into an inexpensive, available, nontoxic, and renewable carbon feedstock. In this regard, last-generation heterogeneous catalysts are [...] Read more.

The conversion of carbon dioxide into valuable chemicals such as cyclic carbonates is an appealing topic for the scientific community due to the possibility of valorizing waste into an inexpensive, available, nontoxic, and renewable carbon feedstock. In this regard, last-generation heterogeneous catalysts are of great interest owing to their high catalytic activity, robustness, and easy recovery and recycling. In the present review, recent advances on CO₂ cycloaddition to epoxide mediated by hybrid catalysts through organometallic or organo-catalytic species supported onto silica-, nanocarbon-, and metal–organic framework (MOF)-based heterogeneous materials, are highlighted and discussed. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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12 pages, 1104 KiB

Open AccessReview

Highlights of Major Progress on Single-Atom Catalysis in 2017

by Yalin Guo, Rui Lang and Botao Qiao

Catalysts 2019, 9(2), 135; https://doi.org/10.3390/catal9020135 - 1 Feb 2019

Cited by 24 | Viewed by 6644

Abstract

Single-atom catalysis has rapidly progressed during the last few years. In 2017, single-atom catalysts (SACs) were fabricated with higher metal loadings and designed into more delicate structures. SACs also found wide applications in C1 chemical conversion, such as selective oxidation of methane and [...] Read more.

Single-atom catalysis has rapidly progressed during the last few years. In 2017, single-atom catalysts (SACs) were fabricated with higher metal loadings and designed into more delicate structures. SACs also found wide applications in C1 chemical conversion, such as selective oxidation of methane and conversion of carbon dioxide. Both experimental characterizations and computational modeling revealed the presence of tunable interactions between single atom species and their surrounding chemical environment, and thus SACs may be more effective and more stable than their nanoparticle counterparts. In this mini-review, we summarize the major achievements of SACs into three main aspects: (a) the advanced synthetic methodologies, (b) catalytic performance in C1 chemistry, and (c) strong metal-support interaction induced unexpected durability. These accomplishments will shed new light on the recognition of single-atom catalysis and encourage more efforts to explore potential applications of SACs. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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15 pages, 2824 KiB

Open AccessReview

The Mechanism of Adsorption, Diffusion, and Photocatalytic Reaction of Organic Molecules on TiO₂ Revealed by Means of On-Site Scanning Tunneling Microscopy Observations

by Peipei Huo, Parveen Kumar and Bo Liu

Catalysts 2018, 8(12), 616; https://doi.org/10.3390/catal8120616 - 4 Dec 2018

Cited by 7 | Viewed by 4934

Abstract

The interaction of organic molecules and titanium dioxide (TiO₂) plays a crucial role in many industry-oriented applications and an understanding of its mechanism can be helpful for the improvement of catalytic efficiency of TiO₂. Scanning tunneling microscopy (STM) has [...] Read more.

The interaction of organic molecules and titanium dioxide (TiO₂) plays a crucial role in many industry-oriented applications and an understanding of its mechanism can be helpful for the improvement of catalytic efficiency of TiO₂. Scanning tunneling microscopy (STM) has been proved to be a powerful tool in characterizing reaction pathways due to its ability in providing on-site images during the catalytic process. Over the past two decades, many research interests have been focused on the elementary reaction steps, such as adsorption, diffusion, and photocatalytic reaction, occurring between organic molecules and model TiO₂ surfaces. This review collects the recent studies where STM was utilized to study the interaction of TiO₂ with three classes of representative organic molecules, i.e., alcohols, carboxylic acids, and aromatic compounds. STM can provide direct evidence for the adsorption configuration, diffusion route, and photocatalytic pathway. In addition, the combination of STM with other techniques, including photoemission spectroscopy (PES), temperature programmed desorption (TPD), and density functional theory (DFT), have been discussed for more insights related to organic molecules-TiO₂ interaction. Full article

(This article belongs to the Special Issue Sustainable Applications in Surface Chemistry and Catalysis)

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