H2 CO2 Research Articles

Effect of frequency on low temperature synthesis of diamond by pulsed discharge MPCVD

Low-temperature synthesis of diamond has broader application prospects compared to traditional diamond synthesis, but it faces issues such as low deposition rate and poor diamond quality. In this study, CH4–CO–H2 were used as reaction gases, and a pulsed discharge MPCVD apparatus was used to deposit diamond films at a substrate temperature of 400 °C and different frequencies were investigated. The results showed that the deposition rate of the pulse discharge was faster than that of continuous microwave discharge. The fastest deposition rate was observed at 500Hz, and crystal size became finer with increasing frequency, while the crystal orientation changed from (100) to (111). A diamond peak at 1333 cm−1 was observed in the Raman spectrum, and the diamond grain size was found to be biggest at 750Hz based on the measured half-width of the peak. Plasma OES analysis revealed that the brightness of CO increased gradually with increasing frequency, while the brightness of H showed an initial increase followed by a decrease. Comparison of emission spectra during low-temperature deposition with a single carbon source showed that CO participated in the reaction for low-temperature diamond synthesis.

Use of Pd-Ag Membrane Reactors for Low-Temperature Dry Reforming of Biogas-A Simulation Study.

Biogas is a valuable renewable energy source that can help mitigate greenhouse emissions. The dry reforming of methane (DRM) offers an alternative hydrogen production route with the advantage of using two main greenhouse gases, CO2 and CH4. However, its real application is limited mainly due to catalyst deactivation by coke formation and the reverse water gas shift (RWGS) reaction that can occur in parallel. Additionally, the typical dry reforming temperature range is 700-950 °C, often leading to catalyst sintering. A low-temperature DRM process could be in principle achieved using a membrane reactor (MR) to shift the dry reforming equilibrium forward and inhibit the RWGS reaction. In this work, biogas reforming was investigated through the simulation of MRs with thin (3.4 µm) and thick (50 µm) Pd-Ag membranes. The effects of the feed temperature (from 450 to 550 °C), pressure (in the range of 2-20 bar), and biogas composition (CH4/CO2 molar ratios from 1/1 to 7/3) were studied for the thin membrane through the calculation and comparison of several process indicators, namely CH4 and CO2 conversions, H2 yield, H2/CO ratio and H2 recovery. Estimation of the CO-inhibiting effect on the H2 molar flux through the membrane was assessed for a thick membrane. Simulations for a thin Pd-Ag MR show that (i) CO2 and CH4 conversions and H2 yield increase with the feed temperature; (ii) H2 yield and average rate of coke formation increase for higher pressures; and (iii) increasing CH4/CO2 feed molar ratio leads to higher H2/CO ratios, but lower H2 yields. Moreover, simulations for a thick Pd-Ag MR showed that the average H2 molar flux decreases due to the CO inhibiting effect (ca. 15%) in the temperature range considered. In conclusion, this work showed that for the considered simulation conditions, the use of an MR leads to the inhibition of the RWGS reaction and improves H2 yield, but coke formation and CO inhibition on H2 permeation may pose limitations on its practical feasibility, for which proper strategies must be explored.

Recent Advances in Transition Metal Phosphide Nanocatalysts for H2 Evolution and CO2 Reduction

Green hydrogen energy has captivated researchers and is regarded as a feasible option for future energy-related aspirations. The emerging awareness of renewable energy-driven hydrogen generation and carbon dioxide reduction calls for the use of unconventional schematic tools in the fabrication of nanocatalyst systems. Transition metal phosphides are state-of-art, cost-effective, noble-metal-free materials that have been comprehensively examined for sustainable energy-driven applications. Recent reports on these advanced functional materials have cemented their candidature as high-performance catalytic systems for hydrogen production and for carbon dioxide conversion into value-added chemical feedstock. Bimetallic NiCoP (238.2 mmol g−1 h−1) exhibits top-notch catalytic competence toward photocatalytic HER that reveals the energy-driven application of a pristine class of TMPs, whereas heterostructured Ni2P/CdS was found to be fit for photochemical CO2 reduction, as well as for HER. On the other hand, pristine Ni2P was recently ascertained as an efficient electrocatalytic system for HER and CO2RR applications. A wide array of physicochemical modulations, such as compositional and structural engineering, defect generation, and facet control, have been used for improving the catalytic efficiency of transition metal phosphide nanostructures. In this review, we succinctly discuss the proficiency of transition metal phosphides in green hydrogen production and carbon dioxide conversion via photochemical and electrochemical pathways. We detail the significance of their structural properties and brief the readers about the synthetic advancements without deviating from our goal of summarizing the recent achievements in energy-driven applications.

Hydrogen-rich syngas production via sorption-enhanced steam gasification of biomass using FexNiyCaO bi-functional materials

Sorption-enhanced steam gasification (SESG) of biomass using Ca-based materials is a promising technology for H2 production and in-situ CO2 capture. Herein, FexNiyCaO bi-functional materials were prepared from carbide slag and used for hydrogen-rich syngas production in a two-stage fixed-bed system with continuous biomass feeding. The results showed that the Fe-doped CaO exhibited better catalytic activity on the water gas shift reaction than Ni-doped CaO, while the Ni-doped CaO was more favorable to steam reforming of tar than Fe-doped CaO. Besides, bimetallic Fe7Ni3CaO possessed the best performance in cyclic CO2 capture capacity, H2 production and catalytic stability among all monometallic and other bimetallic Fe/Ni-doped CaO bi-functional materials. The positive interaction between Fe and Ni alleviated the sintering of Ca2Fe2O5 and improved the resistance of NiO to carbon deposition, thereby improving the catalytic activity and stability of Fe7Ni3CaO. When the catalyst/biomass mass ratio was 3.33, the H2 concentration and H2 yield for Fe7Ni3CaO were 69.2 vol% and 660 mL/g, respectively. Finally, Fe7Ni3CaO exhibited good cyclic stability in H2 production, and the H2 yield of Fe7Ni3CaO was still more than twice that of pure CaO after 5 SESG cycles.

CO2 Capture and H2 Recovery Using a Hollow Fiber Membrane Contactor

In this study, hydrogen was recovered and purified by using a membrane contactor unit from CO2-rich gas without the use of any basic chemicals such as amines. The membrane operational parameters were adjusted to achieve high CO2 removal and H2 recovery. The effects of gas flow rate, pressure, gas composition (CO2/H2 ratio), pressure difference between liquid and gas, and gas/liquid ratio on CO2 removal and H2 recovery were investigated. Depending on the gas flow rate, the contact time between gas and liquid could be controlled, changing the absorption amounts of CO2 and H2. Regarding gas composition, an increase in the CO2/H2 ratio from 0.25 to 1 boosted H2 recovery. Furthermore, increasing the CO2/H2 ratio above 1 (from 1 to 3) generally reduced H2 recovery from 98.7% to 83%. Additionally, supplementation with the optimal amount of additive enhanced CO2 removal and H2 recovery. Thus, using a membrane contactor system results in high CO2 removal (82.7–93.5%) and H2 recovery (91.5–98.7%). Moreover, H2 production and separation can be performed in one system, implying that CO2 removal can be performed more efficiently by the membrane contactor. This study offers a new and promising route for producing high-purity H2 while removing CO2.

Embedding Nano-Piezoelectrics into Heterointerfaces of S-Scheme Heterojunctions for Boosting Photocatalysis and Piezophotocatalysis.

Step-scheme (S-scheme) heterojunctions have exhibited great potential in photocatalysis due to their extraordinary light harvesting and high redox capacities. However, inadequate S-scheme recombination of useless carriers in weak redox abilities increases the probability of their recombination with useful ones in strong redox capabilities. Herein, a versatile protocol is demonstrated to overcome this impediment based on the insertion of nano-piezoelectrics into the heterointerfaces of S-scheme heterojunctions. Under light excitation, the piezoelectric inserter promotes interfacial charge transfer and produces additional photocarriers to recombine with useless electrons and holes, ensuring a more thorough separation of powerful ones for CO2 reduction and H2 O oxidation. When introducing extra ultrasonic vibration, a piezoelectric polarization field is established, which allows efficient separation of charges generated by the embedded piezoelectrics and expedites their recombination with weak carriers, further increasing the number of strong ones participating in the redox reactions. Encouraged by the greatly improved charge utilization, significantly enhanced photocatalytic and piezophotocatalytic activities in CH4 , CO, and O2 production are achieved by the designed stacked catalyst. This work highlights the importance in strengthening the necessary charge recombination in S-scheme heterojunctions and presents an efficient and novel strategy to synergize photocatalysis and piezocatalysis for renewable fuels and value-added chemicals production.

Covalent Organic Frameworks Based Heterostructure in Solar‐To‐Fuel Conversion

AbstractPhotocatalytic reactions for fuel generation are crucial for the world's energy needs. Covalent‐Organic‐Frameworks (COFs) have been extensively studied as promising designable photocatalysts for these reactions due to their efficient visible‐light absorption, suitable energy‐band structure, facilitated intramolecular charge separation, and fast mass transfer. However, the activities of pristine COFs remain unsatisfactory, due to intermolecular charge recombination. Recently, COF‐based heterostructures, which combine COFs with metal‐sulfides, metal‐oxides, carbon materials, or MOFs, have attracted increasing attention for enhancing solar‐to‐fuel conversion efficiency by facilitating interfacial photo‐generated carrier separation, sensitizing wide‐gap semiconductors, and promoting surface redox reactions. Thus, a review of the state‐of‐the‐art progress of COF‐based heterostructure photocatalysts in reactions such as H2 evolution, CO2 reduction, O2 evolution, H2O splitting and CO2 splitting is crucial for the design of new photocatalysts to promote solar‐to‐fuel conversion. In this review, the COF‐based heterostructures photocatalysts are highlighted based on their synthesis, properties, and reasons for enhanced activities. Moreover, design principles are raised for such photocatalysts for each fuel generation reaction, based on insights into related research. Finally, this review is concluded by proposing future trends for COF‐based heterostructures photocatalysts, with attention to the design of COFs and supports, analyzing the photocatalytic reaction dynamics, together with considering practical applications.

Easily Scalable Shell‐Structured Copper Catalyst with High Activity and Durability for Carbon Dioxide Hydrogenation

AbstractInducing strong metal‐support interaction (SMSI) has been a useful way to control the structure of surface active sites. The SMSI often causes the encapsulation of metal particles with an oxide layer. Herein, an amorphous ceria shell was formed on Cu nanoparticles under a mild gas condition with high activity and durability for surface reaction. Cu−Ce solid solution promoted the transfer of surface oxygen species, which induced the ceria shell formation on Cu nanoparticles. This catalyst was used for CO2 hydrogenation, selectively producing CO with high low‐temperature activity and good durability for operation at high temperature. CO2 activation and H2 spillover could occur at low temperatures, enhancing the activity. The shell prevented the sintering, assuring durability. This catalyst was applied to a bench‐scale reactor without loss in performance, resulting in high CO productivity in all temperature ranges.

Easily Scalable Shell-Structured Copper Catalyst with High Activity and Durability for Carbon Dioxide Hydrogenation.

Inducing strong metal-support interaction (SMSI) has been a useful way to control the structure of surface active sites. The SMSI often causes the encapsulation of metal particles with an oxide layer. Herein, an amorphous ceria shell was formed on Cu nanoparticles under a mild gas condition with high activity and durability for surface reaction. Cu-Ce solid solution promoted the transfer of surface oxygen species, which induced the ceria shell formation on Cu nanoparticles. This catalyst was used for CO2 hydrogenation, selectively producing CO with high low-temperature activity and good durability for operation at high temperature. CO2 activation and H2 spillover could occur at low temperatures, enhancing the activity. The shell prevented the sintering, assuring durability. This catalyst was applied to a bench-scale reactor without loss in performance, resulting in high CO productivity in all temperature ranges.

Theoretical Investigation of the Electrochemical Oxidation of H2 and CO Fuels on a Ruddlesden-Popper SrLaFeO4-δ Anode.

The electrochemical oxidation of H2 and CO fuels have been investigated on the Ruddlesden-Popper layered perovskite SrLaFeO4-δ (SLF) under anodic solid oxide fuel cell conditions using periodic density functional theory and microkinetic modeling techniques. Two distinct FeO2-plane-terminated surface models differing in terms of the underlying rock salt layer (SrO or LaO) are used to identify the active site and limiting factors for the electro-oxidation of H2, CO, and syngas fuels. Microkinetic modeling predicted an order of magnitude higher turnover frequency for the electro-oxidation of H2 compared to CO for SLF at short-circuit conditions. The surface model with an underlying SrO layer was found to be more active with respect to H2 oxidation than the LaO-based surface model. At an operating voltage of less than 0.7 V, surface H2O/CO2 formation was found to be the key rate-limiting step, and the surface H2O/CO2 desorption was the key charge transfer step. In contrast, the bulk oxygen migration process was found to affect the overall rate at high cell voltage conditions above 0.9 V. In the presence of syngas fuel, the overall electrochemical activity is derived mainly from H2 electro-oxidation and CO2 is chemically shifted to CO via the reverse water-gas shift reaction. Substitutional doping of a surface Fe atom with Co, Ni, and Mn revealed that the H2 electro-oxidation activity of FeO2-plane terminated anodes with an underlying LaO rock salt layer can be improved with dopant introduction, with Co yielding a three orders of magnitude higher activity relative to the undoped LaO surface model. Constrained ab initio thermodynamic analysis furthermore suggested that the SLF anodes are resistant toward sulfur poisoning both in the presence and absence of dopants. Our findings reflect the role of various elements in controlling the fuel oxidation activity of SLF anodes that could aid the development of new Ruddlesden-Popper phase materials for fuel cell applications.

Sub-Millisecond Laser-Irradiation-Mediated Surface Restructure Boosts the CO Production Yield of Cobalt Oxide Supported Pd Nanoparticles.

The catalytic conversion of CO2 into valuable commodities has the potential to balance ongoing energy and environmental issues. To this end, the reverse water-gas shift (RWGS) reaction is a key process that converts CO2 into CO for various industrial processes. However, the competitive CO2 methanation reaction severely limits the CO production yield; therefore, a highly CO-selective catalyst is needed. To address this issue, we have developed a bimetallic nanocatalyst comprising Pd nanoparticles on the cobalt oxide support (denoted as CoPd) via a wet chemical reduction method. Furthermore, the as-prepared CoPd nanocatalyst was exposed to sub-millisecond laser irradiation with per-pulse energies of 1 mJ (denoted as CoPd-1) and 10 mJ (denoted as CoPd-10) for a fixed duration of 10 s to optimize the catalytic activity and selectivity. For the optimum case, the CoPd-10 nanocatalyst exhibited the highest CO production yield of ∼1667 μmol g-1catalyst, with a CO selectivity of ∼88% at a temperature of 573 K, which is a 41% improvement over pristine CoPd (~976 μmol g-1catalyst). The in-depth analysis of structural characterizations along with gas chromatography (GC) and electrochemical analysis suggested that such a high catalytic activity and selectivity of the CoPd-10 nanocatalyst originated from the sub-millisecond laser-irradiation-assisted facile surface restructure of cobalt oxide supported Pd nanoparticles, where atomic CoOx species were observed in the defect sites of the Pd nanoparticles. Such an atomic manipulation led to the formation of heteroatomic reaction sites, where atomic CoOx species and adjacent Pd domains, respectively, promoted the CO2 activation and H2 splitting steps. In addition, the cobalt oxide support helped to donate electrons to Pd, thereby enhancing its ability of H2 splitting. These results provide a strong foundation to use sub-millisecond laser irradiation for catalytic applications.

Porous Host-Guest MOF-Semiconductor Hybrid with Multisites Heterojunctions and Modulable Electronic Band for Selective Photocatalytic CO2 Conversion and H2 Evolution.

Optimizing catalysts for competitive photocatalytic reactions demand individually tailored band structure as well as intertwined interactions of light absorption, reaction activity, mass, and charge transport. Here, a nanoparticulate host-guest structure is rationally designed that can exclusively fulfil and ideally control the aforestated uncompromising requisites for catalytic reactions. The all-inclusive model catalyst consists of porous Co3 O4 host and Znx Cd1- x S guest with controllable physicochemicalproperties enabled by self-assembled hybrid structure and continuously amenable band gap. The effective porous topology nanoassembly, both at the exterior and the interior pores of a porous metal-organic framework (MOF), maximizes spatially immobilized semiconductor nanoparticles toward high utilization of particulate heterojunctions for vital charge and reactant transfer. In conjunction, the zinc constituent band engineering is found to regulate the light/molecules absorption, band structure, and specific reaction intermediates energy to attain high photocatalytic CO2 reduction selectivity. The optimal catalyst exhibits a H2 -generation rate up to 6720µmol g-1 h-1 and a CO production rate of 19.3µmol g-1 h-1 . These findings provide insight into the design of discrete host-guest MOF-semiconductor hybrid system with readily modulated band structures and well-constructed heterojunctions for selective solar-to-chemical conversion.

In situ construction of cyano-modified g-C3N4 nanolayer-coated SrTiO3 nanotubes by gas-solid reaction for efficient photocatalytic solar fuel production

For the transformation of the global energy structure, photocatalyst-based artificial photosynthesis for solar-to-chemical energy conversion has been regarded as promising. Herein, we report the homogenous construction of cyano-modified g-C3N4 ultrathin nanolayers onto SrTiO3 nanotubes using a simple one-step gas–solid reaction, as well as their application to photocatalytic H2 evolution and CO2 reduction. The creation of one-dimensional core–shell nanostructures and type II heterojunctions broaden visible light absorption range and shorten charge transfer path. The electron-absorbing cyano introduced in situ without any auxiliary salts can not only provide an appropriate driving force for electron transport and extend the active site of photocatalytic reaction, but also alter the band gap to accomplish energy band alignment. Moreover, in-situ irradiation X-ray photoelectron spectroscopy (ISI-XPS) was used to confirm the dual active site system consisting of cyano and SrTiO3. This work aims to promote the development of the surface modification of core-shell nanostructured photocatalysts.

Advanced physical model of hydrothermic reduction of iron ore pellets by dissociated 2H+ ionic gas in the shaft furnace

ABSTRACT Development of various alternative routes for the direct reduction of iron-ore (DRI) and production of sponge irons becomes a necessity today to reduce carbon dioxide (CO2) gas emissions in industrial iron & steel (I&S) making processes. Therefore, the main objective of this work is focused to reduce the carbon footprint in DRI production by eliminating fossil fuel consumption. The reduced iron could be used to melt in the electric arc furnace (EAF) to produce liquid steel by minimising direct scrap addition. Indeed, this paper shows an advanced physical model of a hydrogen fuel shaft furnace for the direct reduced iron-making process by fundamental development of technology with essential modifications in its working principle. This processing technology is hypothetically designed with knowledge of theoretical literature inputs and wisdom of iron and steel-making experience. In this model of a shaft furnace, a scientific approach is designed based on the dissociation of molecular-hydrogen gas (H2+) obtained by water electrolysis and ionisation of the hydrogen gas (2H+) and is incorporated for a high degree of gas adsorption and metallisation during chemical reduction of iron ore (Fe2O3) pellets. The steps involved in the working principle of the new design shaft furnace are simulated and modelled suitably for the existing Midrex furnace operation, which is generally used for DRI production. This approach could be tried using 100% dissociated hydrogen ionic gas (2H+, H+) for future direct reduced iron making by water electrolysis and hydrogen ionisation. Moreover, the reformed reducing gases (CH4–H2–CO) used in the Midrex process can be replaced by the ionised hydrogen gases as an advancement.

Boosting hydrogen production via deoxygenation-sorption-enhanced biomass gasification

Gasification is one of the most promising approaches to accomplishing efficient utilization of biomass, nevertheless, it shows severe problems of low efficiency and syngas quality, which deserves further improvements. In this regard, deoxygenation-sorption-enhanced biomass gasification is proposed and experimentally explored using deoxidizer-decarbonizer materials (xCaO-Fe) for intensified hydrogen production. The materials follow the deoxygenated looping of Fe0-3e−↔Fe3+ as an electron donor and the decarbonized looping of CaO + CO2 ↔ CaCO3 as a CO2 sorbent. Specifically, the H2 yield and CO2 concentration reach 7.9 mmol·g−1 biomass and 10.5 vol%, which increases by 311% and decreases by 75%, respectively, compared with conventional gasification, confirming the promotion effect of deoxygenation-sorption enhancement. Fe embedded within the CaO phase is successfully constructed with the formation of functionalized interface structure, affirming the strong interaction between CaO and Fe. This study brings in a new concept for biomass utilization via synergistic deoxygenation and decarbonization, which will substantially boost high-quality renewable hydrogen production.

Modulating the Interlayer Stacking of Covalent Organic Frameworks for Efficient Acetylene Separation.

Controllable modulation of the stacking modes of 2D (two-dimensional) materials can significantly influence their properties and functionalities but remains a formidable synthetic challenge. Here, an effective strategy is proposed to control the layer stacking of imide-linked 2D covalent organic frameworks (COFs) by altering the synthetic methods. Specifically, a modulator-assisted method can afford a COF with rare ABC stacking without the need for any additives, while solvothermal synthesis leads to AA stacking. The variation of interlayer stacking significantly influences their chemical and physical properties, including morphology, porosity, and gas adsorption performance. The resultant COF with ABC stacking shows much higher C2 H2 capacity and selectivity over CO2 and C2 H4 than the COF with AA stacking, which is not demonstrated in the COF field yet. Furthermore, the outstanding practical separation ability of ABC stacking COF is confirmed by breakthrough experiments of C2 H2 /CO2 (50/50, v/v) and C2 H2 /C2 H4 (1/99, v/v), which can selectively remove C2 H2 with good recyclability. This work provides a new direction to produce COFs with controllable interlayer stacking modes.

Recent Advances in Carbon Nitride-Based S-scheme Photocatalysts for Solar Energy Conversion.

Energy shortages are a major challenge to the sustainable development of human society, and photocatalytic solar energy conversion is a potential way to alleviate energy problems. As a two-dimensional organic polymer semiconductor, carbon nitride is considered to be the most promising photocatalyst due to its stable properties, low cost, and suitable band structure. Unfortunately, pristine carbon nitride has low spectral utilization, easy recombination of electron holes, and insufficient hole oxidation ability. The S-scheme strategy has developed in recent years, providing a new perspective for effectively solving the above problems of carbon nitride. Therefore, this review summarizes the latest progress in enhancing the photocatalytic performance of carbon nitride via the S-scheme strategy, including the design principles, preparation methods, characterization techniques, and photocatalytic mechanisms of the carbon nitride-based S-scheme photocatalyst. In addition, the latest research progress of the S-scheme strategy based on carbon nitride in photocatalytic H2 evolution and CO2 reduction is also reviewed. Finally, some concluding remarks and perspectives on the challenges and opportunities for exploring advanced nitride-based S-scheme photocatalysts are presented. This review brings the research of carbon nitride-based S-scheme strategy to the forefront and is expected to guide the development of the next-generation carbon nitride-based S-scheme photocatalysts for efficient energy conversion.

ZnxZrO2+x-Based Photocatalyst with Dual Active Sites for Tunable Syngas Production from CO2 Photoreduction

Photocatalytic reduction of CO2 in H2O to CO and H2 for syngas production is an attractive option to solve global warming and generate a feedstock for the Fischer–Tropsch process. The syngas generated from CO2 photoreduction with a precise and controllable ratio of H2/CO remains a major challenge to date. In this work, CdS-sensitized nanoscale ZnxZrO2+x solid solutions with dual active sites were synthesized as photocatalysts for tunable syngas H2 and CO production from CO2 photoreduction. The staggered band energy alignments, electron paramagnetic resonance results, and the site of palladium/gold nanoparticles by photodeposition indicate that the charge transfer in the CdS/ZnxZrO2+x heterojunction mainly follows the conventional type II mechanism. Density functional theoretical calculation results reveal that Zn and Zr sites on ZnxZrO2+x are favorable for the adsorption of H2O and CO2 molecules and generation of H2 and CO, respectively. The H2/CO ratio can be controlled in the range from 0.9 to 25.0 by adjusting the content of Zn in ZnxZrO2+x. Moreover, syngas production can be further improved by the modification of Pd nanoparticles. For the first time, this work proposes a strategy to construct a photocatalyst with dual active sites for effectively controlling the H2/CO ratio in syngas synthesis through a fundamental understanding of adsorption and catalytic reaction sites in both H2 evolution and CO2 reduction reactions.

Feed Effects on Water–Gas Shift Activity of M/Co3O4-ZrO2 (M = Pt, Pd, and Ru) and Potassium Role in Methane Suppression

Water–gas shift (WGS) is an industrial process to tackle CO abatement and H2 upgradation. The syngas (CO and H2 mixture) obtained from steam or dry reformers often has unreacted (from dry reforming) or undesired (from steam reforming) CO2, which is subsequently sent to downstream WGS reactor for H2 upgradation. Thus, industrial processes must deal with CO2 and H2 in the reformate feed. Achieving high CO2 or H2 selectivities become challenging due to possible CO and CO2 methanation reactions, which further increases the separation costs to produce pure H2. In this study, M/Co3O4-ZrO2 (M = Ru, Pd and Pt) catalysts were prepared using sonochemical synthesis. The synthesized catalysts were tested for WGS activity under three feed conditions, namely, Feed A (CO and steam), Feed B (CO, H2 and steam) and Feed C (CO, H2, CO2 and steam). All the catalysts gave zero methane selectivity under Feed A conditions, whereas the methane selectivity was significant under Feed B and C conditions. Among all catalysts, PtCZ was found to be the best performing catalyst in terms of CO conversion and CO2 selectivity. However, it still suffered with low but significant methane selectivity. This best performing catalyst was further modified with an alkali component, potassium to suppress undesirable methane selectivity. All the catalysts were well characterized with BET, SEM, TEM to confirm the structural properties and effective doping of the noble metals. Additionally, the apparent activation energies were obtained to showcase the best catalyst.

Construction of porous Ni2P cocatalyst and its promotion effect on photocatalytic H2 production reaction and CO2 reduction

Due to superior light absorption abilities, porous materials are suitable to be served in photocatalytic reactions. In this study, porous Ni2P is target-constructed from porous Ni(OH)2 nanoflower. Promotion effect of the porous Ni2P as cocatalyst is confirmed on photocatalytic performance of Ni2P/CdS composite. The constructed porous Ni2P/CdS photocatalyst shows much higher photocatalytic H2 evolution rate (111.3 mmol h−1 g−1) from water and much higher CO (178.0 μmol h−1 g−1) and CH4 (61.2 μmol h−1 g−1) evolution rates from CO2 reduction than non-porous Ni2P/CdS photocatalyst. Characterizations including UV-Vis diffuse reflectance, photoluminescence, transient photocurrent response, electrochemical impedance and electron paramagnetic resonance are conducted to verify the role of porous Ni2P cocatalyst. The slow photon effect derived from porous structure Ni2P is found to improve light path and increase the absorption utilization of light. The enhanced photocurrent intensity and the lowered resistance of porous Ni2P/CdS due to the formed heterojunctions indicate much rapid isolation of photogenerated electron-hole pairs and rapid charge transfer of electrons. The higher signal of ⋅O2- radicals is detected in porous Ni2P/CdS than non-porous Ni2P/CdS, which result in the remarkable photocatalyst activities of porous Ni2P/CdS. Reaction mechanisms over Ni2P/CdS photocatalyst are illustrated with a Z-scheme charge transfer path.