Cu supported Fe-SiO2 nanocomposites for reverse water gas shift reaction

Solid Solution Derived Cu Clusters on Partially Reduced CuCeO2 with Abundant Oxygen Vacancies Enable Efficient Reverse Water Gas Reaction

The reverse water gas shift (RWGS) reaction provides a convenient approach to convert CO2 to CO, which facilitates to achieve the goals of carbon peaking and carbon neutrality. Herein, the Cu/CeO2 catalyst prepared by a co-precipitation method using a mixture of Na2CO3 and NaOH at pH of 10 (sample Cu/CeO2-10) achieved an intrinsic reaction rate of 428.4 mmol ⋅ gcat -1 ⋅ h-1 with 100 % CO selectivity at 400 °C and CO2/H2 ratio of 1 : 4, which is much higher than Cu/CeO2 prepared by impregnation and other methods. Various characterizations showed the highest fraction of CuCeO2 solid solution in the calcined Cu/CeO2-10, and formed highly dispersed Cu clusters (~2.5 nm) on partially reduced CuCeO2 solid solution with abundant of oxygen vacancies upon reduction. The Cu and oxygen vacancies facilitates the activation of H2 and CO2, respectively, resulting in lowered H2 and CO2 reaction orders. As a result, the synergy between the two components enhanced the overall RWGS activity with lowered activation energy. Moreover, the optimal catalyst is very stable in 24 h stability test without detectable agglomeration of Cu clusters.

Recent Advances in Hydrogenation of CO2 to CO with Heterogeneous Catalysts Through the RWGS Reaction

With the continuous increase in CO2 emissions, primarily from the combustion of coal and oil, the ecosystem faces a significant threat. Therefore, as an effective method to minimize the issue, the Reverse Water Gas Shift (RWGS) reaction which converts CO2 towards CO attracts much attention, is an environmentally-friendly method to mitigate climate change and lessen dependence on fossil fuels. Nevertheless, the inherent thermodynamic stability and kinetic inertness of CO2 is a big challenge under mild conditions. In addition, it remains another fundamental challenge in RWGS reaction owing to CO selectivity issue caused by CO2 further hydrogenation towards CH4 . Up till now, a series of catalysis systems have been developed for CO2 reduction reaction to produce CO. Herein, the research progress of the well-performed heterogeneous catalysts for the RWGS reaction were summarized, including the catalyst design, catalytic performance and reaction mechanism. This review will provide insights into efficient utilization of CO2 and promote the development of RWGS reaction.

Design of Cu/MoOx for CO2 Reduction via Reverse Water Gas Shift Reaction

CO2 reduction to CO as raw material for conversion to chemicals and gasoline fuels via the reverse water–gas shift (RWGS) reaction is generally acknowledged to be a promising strategy that makes the CO2 utilization process more economical and efficient. Cu-based catalysts are low-cost and have high catalytic performance but have insufficient stability due to hardening at high temperatures. In this work, a series of Cu-based catalysts supported by MoOx were synthesized for noble metal-free RWGS reactions, and the effects of MoOx support on catalyst performance were investigated. The results show that the introduction of MoOx can effectively improve the catalytic performance of RWGS reactions. The obtained Cu/MoOx (1:1) catalyst displays excellent activity with 35.85% CO2 conversion and 99% selectivity for CO at 400 °C. A combination of XRD, XPS, and HRTEM characterization results demonstrate that MoOx support enhances the metal-oxide interactions with Cu through electronic modification and geometric coverage, thus obtaining highly dispersed copper and more Cu-MoOx interfaces as well as more corresponding oxygen vacancies.

Reverse water gas shift reaction over a Cu/ZnO catalyst supported on regenerated spent bleaching earth (RSBE) in a slurry reactor: the effect of the Cu/Zn ratio on the catalytic activity

The catalytic conversion of CO2 via the Reverse Water Gas Shift (RWGS) reaction for CO production is a promising environment-friendly approach. The greenhouse gas emissions from burning fossil fuels can be used to produce valuable fuels or chemicals through CO2 hydrogenation. Therefore, this project was to study the CO2 conversion via RWGS over various Cu/ZnO catalysts supported by regenerated spent bleaching earth (RSBE) prepared by wet impregnation technique with different Cu : Zn ratios (0.5, 1.0, 1.5, 2.0, 3.0). The causes of environmental pollution from the disposal of spent bleaching earth (SBE) from an edible oil refinery can be eliminated by using it as catalyst support after the regeneration process. The synthesized catalysts were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), temperature-programmed reduction of hydrogen (TPR-H2), pyridine-adsorbed Fourier transform infrared (FTIR-pyridine), temperature programmed desorption of carbon dioxide (TPD-CO2), N2 physisorption, and Fourier transform infrared (FTIR) analysis. The RWGS reaction was carried out in a slurry reactor at 200 °C, with a pressure of 3 MPa, a residence time of 4 h, and catalyst loading of 1.0 g with an H2/CO2 ratio of 3. According to experimental data, the Cu/Zn ratio significantly impacts the catalytic structure and performance. The catalytic activity increased until the Cu : Zn ratio reached the maximum value of 1.5, while a further increase in Cu/Zn ratio inhibited the catalytic performance. The CZR3 catalyst (Cu/Zn ratio of 1.5) with a higher catalytic reducibility, high copper dispersion with small crystalline size, lower total pore volume as well as higher basicity showed superior catalytic performance in terms of CO2 conversion (40.67%) and CO yield (39.91%). Findings on the effect of reaction conditions revealed that higher temperature (>240 °C), higher pressure (>3 MPa), higher reaction time (>4 h) and higher catalyst loading (>1.25 g) could improve CO2 conversion to CO yield. A maximum CO2 conversion of 45.8% and multiple recycling stability of the catalyst were achieved, showing no significant decrease in CO2 conversion.

Photothermal synthesis of a CuO x &FeO y catalyst with a layered double hydroxide-derived pore-confined frame to achieve photothermal CO2 hydrogenation to CO with a rate of 136 mmol min-1 gcat -1

Solar-driven CO₂ conversion into the industrial chemical CO via the reverse water-gas reaction is an ideal technological approach to achieve the key step of carbon neutralization. The high reaction temperature is cost-free due to the photothermal conversion brought about by solar irradiation and is beneficial to the catalytic efficiency. However, the thermostability of adopted catalysts is a great challenge. Herein, we develop an in situ photothermal synthesis to obtain a CuO _x &FeO _y catalyst with a layered double hydroxide-derived pore-confined frame. The optimized sample delivers a CO generation rate of 136.3 mmol min^-1 g_cat ^-1 with the selectivity of ∼100% at a high reaction temperature of 1015 °C. The efficient catalytic activity can be attributed to the fact that the pore-confined frame substrate prevents the growth of CuO _x and FeO _y nanoparticles during the high-temperature reaction and the basic groups on the substrate promote the adsorption and activation of CO₂.

Designing FeO@graphite@C Nanocomposites Based on Humins as Efficient Catalysts for Reverse Water-Gas Shift

Acid-catalyzed conversion of biomass into bio-based platform chemicals such as levulinic acid and 5-hydroxymethylfurfural is an important route in biorefineries, which has attracted much attention in recent years. Such a route however unavoidably yields massive recalcitrant byproducts called humins, which are now broadly considered as waste and are limited to combustion, causing unfavorable energy and environmental processes. Therefore, the development of a value-added utilization approach for such humin byproducts is crucial for making the biorefineries economical and environmentally viable. In this work, we present a starting point for valorization of humins via the preparation of carbon-based iron oxide nanocomposites of FeO@graphite@C by using the humins as carbon resources and material templates via a facile synthesis strategy. The as-prepared catalyst is capable of promoting the reverse water-gas shift reaction and reaching a high CO₂ conversion ratio with excellent CO selectivity (> 99%) at 500-700 °C, enabling an efficient utilization of waste CO₂. The unique graphite-capsuled FeO structure of FeO@graphite@C was found to be the origin of its excellent catalytic activity toward CO₂ reduction into CO, which shifts electrons from the graphite layer to FeO, reconstructing the Fe electron structure. This strengthened the electrophilic attack ability toward CO₂ and weakened the bond with the derived CO* species of the Fe active sites, associated with the excellent CO₂ conversion and CO selectivity.

Nickel Phosphide Catalysts as Efficient Systems for CO2 Upgrading via Dry Reforming of Methane

This work establishes the primordial role played by the support’s nature when aimed at the constitution of Ni2P active phases for supported catalysts. Thus, carbon dioxide reforming of methane was studied over three novel Ni2P catalysts supported on Al2O3, CeO2 and SiO2-Al2O3 oxides. The catalytic performance, shown by the catalysts’ series, decreased according to the sequence: Ni2P/Al2O3 > Ni2P/CeO2 > Ni2P/SiO2-Al2O3. The depleted CO2 conversion rates discerned for the Ni2P/SiO2-Al2O3 sample were associated to the high sintering rates, large amounts of coke deposits and lower fractions of Ni2P constituted in the catalyst surface. The strong deactivation issues found for the Ni2P/CeO2 catalyst, which also exhibited small amounts of Ni2P species, were majorly associated to Ni oxidation issues. Along with lower surface areas, oxidation reactions might also affect the catalytic behaviour exhibited by the Ni2P/CeO2 sample. With the highest conversion rate and optimal stabilities, the excellent performance depicted by the Ni2P/Al2O3 catalyst was mostly related to the noticeable larger fractions of Ni2P species established.