Two-step thermochemical cycles using fibrous ceria pellets for H2 production and CO2 reduction in packed-bed solar reactors

Inspired by the knowledge of the thermocatalytic CO2 reduction process, novel nanocrystalline CuZnAl-oxide based catalysts with pyramidal mesoporous structures are here proposed for the CO2 electrochemical reduction under ambient conditions. The XPS analyses revealed that the co-presence of ZnO and Al2O3 into the Cu-based catalyst stabilize the CuO crystalline structure and introduce basic sites on the ternary as-synthesized catalyst. In contrast, the as-prepared CuZn- and Cu-based materials contain a higher amount of superficial Cu0 and Cu1+ species. The CuZnAl-catalyst exhibited enhanced catalytic performance for the CO and H2 production, reaching a Faradaic efficiency (FE) towards syngas of almost 95% at −0.89 V vs. RHE and a remarkable current density of up to 90 mA cm−2 for the CO2 reduction at −2.4 V vs. RHE. The physico-chemical characterizations confirmed that the pyramidal mesoporous structure of this material, which is constituted by a high pore volume and small CuO crystals, plays a fundamental role in its low diffusional mass-transfer resistance. The CO-productivity on the CuZnAl-catalyst increased at more negative applied potentials, leading to the production of syngas with a tunable H2/CO ratio (from 2 to 7), depending on the applied potential. These results pave the way to substitute state-of-the-art noble metals (e.g., Ag, Au) with this abundant and cost-effective catalyst to produce syngas. Moreover, the post-reaction analyses demonstrated the stabilization of Cu2O species, avoiding its complete reduction to Cu0 under the CO2 electroreduction conditions.

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Insights into the TiO2-Based Photocatalytic Systems and Their Mechanisms

Catalysts ◽

10.3390/catal9080680 ◽

2019 ◽

Vol 9 (8) ◽

pp. 680 ◽

Cited By ~ 12

Author(s):

Sakar ◽

Prakash ◽

Do

Keyword(s):

Band Structure ◽

Co2 Reduction ◽

H2 Production ◽

Energy Structure ◽

Energy Applications ◽

Emerging Trends ◽

Recent Developments ◽

Carrier Separation ◽

Photocatalytic Applications ◽

Photocatalytic Materials

Photocatalysis is a multifunctional phenomenon that can be employed for energy applications such as H2 production, CO2 reduction into fuels, and environmental applications such as pollutant degradations, antibacterial disinfection, etc. In this direction, it is not an exaggerated fact that TiO2 is blooming in the field of photocatalysis, which is largely explored for various photocatalytic applications. The deeper understanding of TiO2 photocatalysis has led to the design of new photocatalytic materials with multiple functionalities. Accordingly, this paper exclusively reviews the recent developments in the modification of TiO2 photocatalyst towards the understanding of its photocatalytic mechanisms. These modifications generally involve the physical and chemical changes in TiO2 such as anisotropic structuring and integration with other metal oxides, plasmonic materials, carbon-based materials, etc. Such modifications essentially lead to the changes in the energy structure of TiO2 that largely boosts up the photocatalytic process via enhancing the band structure alignments, visible light absorption, carrier separation, and transportation in the system. For instance, the ability to align the band structure in TiO2 makes it suitable for multiple photocatalytic processes such as degradation of various pollutants, H2 production, CO2 conversion, etc. For these reasons, TiO2 can be realized as a prototypical photocatalyst, which paves ways to develop new photocatalytic materials in the field. In this context, this review paper sheds light into the emerging trends in TiO2 in terms of its modifications towards multifunctional photocatalytic applications.

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Sulfide-Based Photocatalysts Using Visible Light, with Special Focus on In2S3, SnS2 and ZnIn2S4

Catalysts ◽

10.3390/catal12010040 ◽

2021 ◽

Vol 12 (1) ◽

pp. 40

Author(s):

José C. Conesa

Keyword(s):

Visible Light ◽

Wavelength Range ◽

Artificial Photosynthesis ◽

Co2 Reduction ◽

H2 Production ◽

Special Focus ◽

Reduction Processes ◽

Photocatalytic Activities ◽

Photocatalytic Processes ◽

Better Than

Sulfides are frequently used as photocatalysts, since they absorb visible light better than many oxides. They have the disadvantage of being more easily photocorroded. This occurs mostly in oxidizing conditions; therefore, they are commonly used instead in reduction processes, such as CO2 reduction to fuels or H2 production. Here a summary will be presented of a number of sulfides used in several photocatalytic processes; where appropriate, some recent reviews will be presented of their behaviour. Results obtained in recent years by our group using some octahedral sulfides will be shown, showing how to determine their wavelength-dependent photocatalytic activities, checking their mechanisms in some cases, and verifying how they can be modified to extend their wavelength range of activity. It will be shown here as well how using photocatalytic or photoelectrochemical setups, by combining some enzymes with these sulfides, allows achieving the photo-splitting of water into H2 and O2, thus constituting a scheme of artificial photosynthesis.

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Syntrophic H2 production enhances the performance of primarily acetate-supplemented reactors treating sulphate contaminated solutions

10.1101/2021.05.12.443249 ◽

2021 ◽

Author(s):

Tomas Hessler ◽

Susan T.L. Harrison ◽

Jillian F. Banfield ◽

Robert J. Huddy

Keyword(s):

Microbial Communities ◽

Packed Bed ◽

H2 Production ◽

Flow Path ◽

Packed Bed Bioreactor ◽

Sulfate Removal ◽

Metabolic Interactions ◽

Fermentative Hydrogen ◽

Biological Sulfate Reduction ◽

The Impact

Biological sulfate reduction (BSR) represents a promising bioremediation strategy, yet the impact of metabolic interactions on performance has been largely unexplored. Here, genome-resolved metagenomics was used to characterise 17 microbial communities associated with reactors operated with defined sulfate-contaminated solutions. Pairs of reactors were supplemented with lactate or with acetate plus a small amount of fermentable substrate. At least thirty draft quality genomes, representing all the abundant bacteria, were recovered from each metagenome. All of the 22 SRB genomes encode genes for H2 consumption. And of the total 163 genomes recovered, 130 encode 321 NiFe and FeFe hydrogenases. The lactate-supplemented packed-bed bioreactor was particularly interesting as it resulted in stratified microbial communities that were distinct in their predominant metabolisms. Pathways for fermentation of lactate and hydrogen production were enriched towards the inlet whereas increased autotrophy and acetate-oxidizing SRB were evident towards the end of the flow path. We hypothesized that high sulfate removal towards the end of the flow path, despite acetate being an electron donor that typically sustains low SRB growth rates, was stimulated by H2 consumption. This hypothesis was supported by sustained performance of the predominantly acetate-supplemented stirred-tank reactor, which was dominated by diverse fermentative, hydrogen-evolving bacteria and low-abundance SRB capable of acetate and hydrogen consumption. We conclude that the performance of BSR reactors supplemented with inexpensive acetate can be improved by the addition of a low concentration of fermentable material due to stimulation of syntrophic relationships among hydrogen-producing non-SRB and dual hydrogen- and acetate-utilising SRB.

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Effect of Operation Conditions on Hydrogen Production by PSB in Immobilized-Cells Packed Bed

ASME 2008 2nd International Conference on Energy Sustainability, Volume 2 ◽

10.1115/es2008-54085 ◽

2008 ◽

Author(s):

Y. Z. Wang ◽

Q. Liao ◽

X. Zhu ◽

X. Tian

Keyword(s):

Production Rate ◽

Immobilized Cells ◽

Packed Bed ◽

H2 Production ◽

Optimal Operation ◽

Organic Substrate ◽

Inlet Temperature ◽

Operation Conditions ◽

Multiple Operation ◽

Operation Factor

Effect of multiple operation conditions on behaviors of H2 production from organic substrate by photo-fermentation in immobilized-cells packed bed using Rhodoseudomonas palustris CQK 01 were investigated in a continuous culture. It revealed that in limited light intensity or below 590 nm of light wavelength the H2 production rate of the immobilized-cells bioreactor increased with increase of value of the experimental parameters. And the optimal operation factor of inlet concentration of substrate and inlet temperature of liquid for H2 production was 50 mmol/L and 30 °C, respectively. However, when these parameters value in the experiment became suppressive conditions the H2 production rate would went down with parameter ascending.

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