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5 pages, 187 KiB

Open AccessEditorial

Catalytic, Photocatalytic, and Electrocatalytic Processes for the Valorization of CO₂

by Ilenia Rossetti and Gianguido Ramis

Catalysts 2019, 9(9), 765; https://doi.org/10.3390/catal9090765 - 12 Sep 2019

Cited by 7 | Viewed by 2406

Abstract

Worldwide yearly CO₂ emissions reached 36 Gt in 2014, whereas they amounted to ca [...] Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

Research

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18 pages, 4254 KiB

Open AccessArticle

High Pressure Photoreduction of CO₂: Effect of Catalyst Formulation, Hole Scavenger Addition and Operating Conditions

by Elnaz Bahadori, Antonio Tripodi, Alberto Villa, Carlo Pirola, Laura Prati, Gianguido Ramis and Ilenia Rossetti

Catalysts 2018, 8(10), 430; https://doi.org/10.3390/catal8100430 - 30 Sep 2018

Cited by 47 | Viewed by 5243

Abstract

The photoreduction of CO₂ is an intriguing process which allows the synthesis of fuels and chemicals. One of the limitations for CO₂ photoreduction in the liquid phase is its low solubility in water. This point has been here addressed by designing [...] Read more.

The photoreduction of CO₂ is an intriguing process which allows the synthesis of fuels and chemicals. One of the limitations for CO₂ photoreduction in the liquid phase is its low solubility in water. This point has been here addressed by designing a fully innovative pressurized photoreactor, allowing operation up to 20 bar and applied to improve the productivity of this very challenging process. The photoreduction of CO₂ in the liquid phase was performed using commercial TiO₂ (Evonink P25), TiO₂ obtained by flame spray pyrolysis (FSP) and gold doped P25 (0.2 wt% Au-P25) in the presence of Na₂SO₃ as hole scavenger (HS). The different reaction parameters (catalyst concentration, pH and amount of HS) have been addressed. The products in liquid phase were mainly formic acid and formaldehyde. Moreover, for longer reaction time and with total consumption of HS, gas phase products formed (H₂ and CO) after accumulation of significant number of organic compounds in the liquid phase, due to their consecutive photoreforming. Enhanced CO₂ solubility in water was achieved by adding a base (pH = 12–14). In basic environment, CO₂ formed carbonates which further reduced to formaldehyde and formic acid and consequently formed CO/CO₂ + H₂ in the gas phase through photoreforming. The deposition of small Au nanoparticles (3–5 nm) (NPs) onto TiO₂ was found to quantitatively influence the products distribution and increase the selectivity towards gas phase products. Significant energy storage in form of different products has been achieved with respect to literature results. Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

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10 pages, 3100 KiB

Open AccessArticle

Effect of In-Situ Dehydration on Activity and Stability of Cu–Ni–K₂O/Diatomite as Catalyst for Direct Synthesis of Dimethyl Carbonate

by Dongmei Han, Yong Chen, Shuanjin Wang, Min Xiao, Yixin Lu and Yuezhong Meng

Catalysts 2018, 8(9), 343; https://doi.org/10.3390/catal8090343 - 23 Aug 2018

Cited by 6 | Viewed by 3830

Abstract

An in-situ dehydrating system built in a continuous flow fixed-bed bubbling reactor for direct synthesis of dimethyl carbonate (DMC) was designed. 3A molecular sieve (MS) was selected as the ideal dehydrating agent and the water trapping efficiency was studied. The effect of dehydrating [...] Read more.

An in-situ dehydrating system built in a continuous flow fixed-bed bubbling reactor for direct synthesis of dimethyl carbonate (DMC) was designed. 3A molecular sieve (MS) was selected as the ideal dehydrating agent and the water trapping efficiency was studied. The effect of dehydrating agent/catalyst ratio, the dehydrating temperature and pressure, as well as the space velocity on the direct DMC synthesis catalyzed by K₂O-promoted Cu–Ni was further investigated. These results demonstrated that 3A MS could effectively dehydrate the reaction system at the optimal conditions of 120 °C and 1.0 MPa with gas space velocity (GHSV) of 600 h⁻¹, thereby greatly shifting the reaction equilibrium toward high DMC yield. Higher DMC yield of 13% was achieved compared with undehydrated reaction. Moreover, the catalyst can be highly stabilized by 3A MS dehydration with stable performs over 22 h. Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

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15 pages, 4233 KiB

Open AccessArticle

Evolution of Water Diffusion in a Sorption-Enhanced Methanation Catalyst

by Renaud Delmelle, Jasmin Terreni, Arndt Remhof, Andre Heel, Joris Proost and Andreas Borgschulte

Catalysts 2018, 8(9), 341; https://doi.org/10.3390/catal8090341 - 21 Aug 2018

Cited by 14 | Viewed by 4313

Abstract

Sorption-enhanced methanation has consequent advantages compared to conventional methanation approaches; namely, the production of pure methane and enhanced kinetics thanks to the application of Le Châtelier’s principle. In this paper, we address the question of the long-term stability of a sorption-enhanced methanation catalyst-support [...] Read more.

Sorption-enhanced methanation has consequent advantages compared to conventional methanation approaches; namely, the production of pure methane and enhanced kinetics thanks to the application of Le Châtelier’s principle. In this paper, we address the question of the long-term stability of a sorption-enhanced methanation catalyst-support couple: Ni nanoparticles on zeolite 5A. Compared to most conventional methanation processes the operational conditions of sorption-enhanced methanation are relatively mild, which allow for stable catalyst activity on the long term. Indeed, we show here that neither coking nor thermal degradation come into play under such conditions. However, a degradation mechanism specific to the sorption catalysis was observed under cyclic methanation/drying periods. This severely affects water diffusion kinetics in the zeolite support, as shown here by a decrease of the water-diffusion coefficient during multiple cycling. Water diffusion is a central mechanism in the sorption-enhanced methanation process, since it is rate-limiting for both methanation and drying. Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

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11 pages, 4245 KiB

Open AccessArticle

Effect of Alkali-Doping on the Performance of Diatomite Supported Cu-Ni Bimetal Catalysts for Direct Synthesis of Dimethyl Carbonate

by Dongmei Han, Yong Chen, Shuanjin Wang, Min Xiao, Yixin Lu and Yuezhong Meng

Catalysts 2018, 8(8), 302; https://doi.org/10.3390/catal8080302 - 27 Jul 2018

Cited by 15 | Viewed by 3707

Abstract

Alkali-adopted Cu-Ni/diatomite catalysts were designed and used for the direct synthesis of dimethyl carbonate (DMC) from carbon dioxide and methanol. Alkali additives were introduced into Cu-Ni/diatomite catalyst as a promoter because of its lower work function (Ni > Cu > Li > Na [...] Read more.

Alkali-adopted Cu-Ni/diatomite catalysts were designed and used for the direct synthesis of dimethyl carbonate (DMC) from carbon dioxide and methanol. Alkali additives were introduced into Cu-Ni/diatomite catalyst as a promoter because of its lower work function (Ni > Cu > Li > Na > K > Cs) and stronger electron-donating ability. A series of alkali-promoted Cu-Ni/diatomite catalysts were prepared by wetness impregnation method with different kind and different loading of alkali. The synthesized catalysts were fully characterized by means of X-ray diffraction (XRD), scanning electron microscope (SEM), temperature-programmed reduction (TPR), and NH₃/CO₂-TPD. The experimental results demonstrated that alkali adoption can significantly promote the catalytic activity of Cu–Ni bimetallic catalysts. Under the catalytic reaction conditions of 120 °C and 1.0 MPa; the highest CH₃OH conversion of 9.22% with DMC selectivity of 85.9% has been achieved when using 15%(2Cu-Ni) 2%Cs₂O/diatomite catalyst (CuO + NiO = 15 wt. %, atomic ratio of Cu/Ni = 2/1, Cs₂O = 2 wt. %). Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

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11 pages, 10463 KiB

Open AccessArticle

Metal-Carbon-CNF Composites Obtained by Catalytic Pyrolysis of Urban Plastic Residues as Electro-Catalysts for the Reduction of CO₂

by Jesica Castelo-Quibén, Abdelhakim Elmouwahidi, Francisco J. Maldonado-Hódar, Francisco Carrasco-Marín and Agustín F. Pérez-Cadenas

Catalysts 2018, 8(5), 198; https://doi.org/10.3390/catal8050198 - 9 May 2018

Cited by 7 | Viewed by 4993

Abstract

Metal–carbon–carbon nanofibers composites obtained by catalytic pyrolysis of urban plastic residues have been prepared using Fe, Co or Ni as pyrolitic catalysts. The composite materials have been fully characterized from a textural and chemical point of view. The proportion of carbon nanofibers and [...] Read more.

Metal–carbon–carbon nanofibers composites obtained by catalytic pyrolysis of urban plastic residues have been prepared using Fe, Co or Ni as pyrolitic catalysts. The composite materials have been fully characterized from a textural and chemical point of view. The proportion of carbon nanofibers and the final content of carbon phases depend on the used pyrolitic metal with Ni being the most active pyrolitic catalysts. The composites show the electro-catalyst activity in the CO₂ reduction to hydrocarbons, favoring all the formation of C1 to C4 hydrocarbons. The tendency of this activity is in accordance with the apparent faradaic efficiencies and the linear sweep voltammetries. The cobalt-based composite shows high selectivity to C3 hydrocarbons within this group of compounds. Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

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10954 KiB

Open AccessArticle

Surface Oxidation of Supported Ni Particles and Its Impact on the Catalytic Performance during Dynamically Operated Methanation of CO₂

by Benjamin Mutz, Andreas Martin Gänzler, Maarten Nachtegaal, Oliver Müller, Ronald Frahm, Wolfgang Kleist and Jan-Dierk Grunwaldt

Catalysts 2017, 7(9), 279; https://doi.org/10.3390/catal7090279 - 18 Sep 2017

Cited by 60 | Viewed by 9467

Abstract

The methanation of CO₂ within the power-to-gas concept was investigated under fluctuating reaction conditions to gather detailed insight into the structural dynamics of the catalyst. A 10 wt % Ni/Al₂O₃ catalyst with uniform 3.7 nm metal particles and a [...] Read more.

The methanation of CO₂ within the power-to-gas concept was investigated under fluctuating reaction conditions to gather detailed insight into the structural dynamics of the catalyst. A 10 wt % Ni/Al₂O₃ catalyst with uniform 3.7 nm metal particles and a dispersion of 21% suitable to investigate structural changes also in a surface-sensitive way was prepared and characterized in detail. Operando quick-scanning X-ray absorption spectroscopy (XAS/QEXAFS) studies were performed to analyze the influence of 30 s and 300 s H₂ interruptions during the methanation of CO₂ in the presence of O₂ impurities (technical CO₂). These conditions represent the fluctuating supply of H₂ from renewable energies for the decentralized methanation. Short-term H₂ interruptions led to oxidation of the most reactive low-coordinated metallic Ni sites, which could not be re-reduced fully during the subsequent methanation cycle and accordingly caused deactivation. Detailed evaluation of the extended X-ray absorption fine structure (EXAFS) spectra showed surface oxidation/reduction processes, whereas the core of the Ni particles remained reduced. The 300-s H₂ interruptions resulted in bulk oxidation already after the first cycle and a more pronounced deactivation. These results clearly show the importance and opportunities of investigating the structural dynamics of catalysts to identify their mechanism, especially in power-to-chemicals processes using renewable H₂. Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

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Review

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35 pages, 12216 KiB

Open AccessReview

Microwave, Ultrasound, and Mechanochemistry: Unconventional Tools that Are Used to Obtain “Smart” Catalysts for CO₂ Hydrogenation

by Maela Manzoli and Barbara Bonelli

Catalysts 2018, 8(7), 262; https://doi.org/10.3390/catal8070262 - 28 Jun 2018

Cited by 14 | Viewed by 5655

Abstract

The most recent progress obtained through the precise use of enabling technologies, namely microwave, ultrasound, and mechanochemistry, described in the literature for obtaining improved performance catalysts (and photocatalysts) for CO₂ hydrogenation, are reviewed. In particular, the main advantages (and drawbacks) found in [...] Read more.

The most recent progress obtained through the precise use of enabling technologies, namely microwave, ultrasound, and mechanochemistry, described in the literature for obtaining improved performance catalysts (and photocatalysts) for CO₂ hydrogenation, are reviewed. In particular, the main advantages (and drawbacks) found in using the proposed methodologies will be discussed and compared by focusing on catalyst design and optimization of clean and efficient (green) synthetic processes. The role of microwaves as a possible activation tool used to improve the reaction yield will also be considered. Full article

(This article belongs to the Special Issue Catalytic, Photocatalytic and Electrocatalytic Processes for the Valorisation of CO₂)

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