To address the ever-increasing CO 2 concentration problem in the atmospheric air arisen by massive consumption of fossil fuels, electrocatalytic technologies that reduce CO 2 to generate high value-added products have been gaining increasing interest. Cu-based CO 2 reduction catalysts have attracted widespread attention owing to their capability of generating C 1 and C 2+ products. However, Cu-based catalysts are highly challenged by their low product selectivity. Recently, Cu-based bimetallic catalysts have been found the unique catalytical activity and selectivity in CO 2 reduction reactions (CO 2 RR). The incorporation of other metals can change the electronic circumstance of Cu-based catalysts, promoting the adsorption ability of the intermediate products and consequently leading to high selectivity. In this minireview, we intend to summarize recent advances of Cu-based bimetallic catalysts in producing C 1 and C 2+ products, involving designing heterostructure, alloy, defects and surface modification engineering. We pay special attention to the regulation of electronic structure of the composite catalysts, as well as insights into the relationship between electronic property and catalytical performance for Cu-based bimetallic catalysts. This article analyzed the influence of the electronic structure of materials on the catalytic performance. Focusing on the application of four methods of Heterostructure Engineering, Alloy Engineering, Defect design Engineering and Surface modification Engineering to Cu-based bimetallic materials, the advantages of electronic regulation of materials and catalyzing CO 2 to generate high-value chemicals. 

Progress in Regulating Electronic Structure Strategies on Cu-Based Bimetallic Catalysts for CO2 Reduction Reaction

Methanation of CO2 using H2 obtained by renewable energy sources has been gaining attention as one of the promising options for utilizing captured CO2 and surplus power obtained when intermittent p...

Determination of Kinetic Parameters for CO2 Methanation (Sabatier Reaction) over Ni/ZrO2 at a Stoichiometric Feed-Gas Composition under Elevated Pressure

Catalytic reduction of CO2 with renewable H2 to CO via the reverse water gas shift (RWGS) reaction is an attractive approach to recycle CO2 and control net emission of CO2 to atmosphere. However, low activity and high CH4 selectivity at low temperatures limited the practical implementation of the reaction. Herein, Pt-Re/SiO2 catalysts with varying amount of Re were prepared with co-impregnation and tested for the RWGS reaction. Characterization results indicated that the oxophilic ReOx (0 ≤ x ≤ 3.5) located in close proximity to Pt particle, modified the surface of Pt by both partial coverage and electronic interaction, resulting in the reduced number of sites for and weakened strength of CO adsorption. At 400 °C, the turnover frequency (2.30 s−1) on the optimal Pt-Re/SiO2 catalyst (Pt/Re = 1.91) is 3.9 times higher than that on Pt/SiO2 under differential conditions, and the apparent activation energy is lowered. In contrast to Re/SiO2 which produces significant amount of CH4, the CO selectivity on Pt-Re/SiO2 maintained > 96.2 % under integral conditions. Reaction order analysis revealed that Pt facilitates H2 activation whereas the oxophilic ReOx enhances CO2 adsorption and activation. The perimeter sites at the Pt/ReOx interface with a balanced hydrogenation and C-O cleavage properties synergistically improve the RWGS activity while inhibiting CH4 production. 

Synergetic enhancement of activity and selectivity for reverse water gas shift reaction on Pt-Re/SiO2 catalysts

For many years, capturing, storing or sequestering CO2 from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO2. Moreover, the use of CO2 as a C1 building block to mitigate CO2 emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO2 into valuable chemicals has received much attention in the last decade, since CO2 is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO2 is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO2 requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO2 conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO2 into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO2 into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C2+OH), C2+ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO2 into chemicals and fuels.

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels.

The production of either CO or CH4 via the hydrogenation of CO2 is amongst the most promising routes for CO2 utilization. However, kinetic barriers necessitate the use of a catalyst, with Ni/CeO2 being one of the most investigated systems. Nevertheless, surface chemistry fine-tuning via appropriate promotional routes can induce significant modifications on the solid-state properties of catalysts and in turn on their activity/selectivity. In the present work, we originally report on the outstanding selectivity alteration of Ni/CeO2 by ZnO doping. Specifically, Ni-based catalysts supported on ZnO, CeO2 nanorods or a mixed ZnO-CeO2 oxide were synthesized by a modified hydrothermal method and characterized by various physicochemical methods. Notable changes in the reaction pathway were demonstrated, as the presence of ZnO largely favored CO production at T < 450 oC for both Ni/ZnO and Ni/ZnO-CeO2, whereas Ni/CeO2 was completely selective to CH4. These findings were interpreted on the basis of ZnO-induced inhibitory effects on key activity/selectivity descriptors like the redox and basic properties, as well as on the adsorption affinity of CO species, which are considered as intermediate species for CO2 methanation. 

Support-induced modifications on the CO2 hydrogenation performance of Ni/CeO2: The effect of ZnO doping on CeO2 nanorods

Catalytic reduction of CO2 to CO via reverse water gas shift (RWGS) reaction provides a feasible approach to utilize CO2, since CO can be further converted to various versatile products through the syngas routes. Ni-based catalysts are low cost and have a high activity for CO2 reduction but are nonselective for RWGS due to competition from methanation. In this work, we demonstrated that surface modification of Ni by MoOx can be tailored to tune the reactions of RWGS and methanation. The addition of MoOx improves Ni dispersion through strong interactions whereas partially reduced MoOx modifies the surface of Ni particles through both geometric coverage and electronic modification. No CO adsorption was observed at room temperature on the NiMo catalyst with a Mo/Ni ratio of 1, confirmed by density functional theory calculation. Tracking product evolution showed that CO2 is first reduced to CO through RWGS on the Ni catalysts and methane is a product of CO hydrogenation. Apparent activation energy analysis indicates that the overall reaction is controlled by CO desorption. Addition of a small amount of Mo (Mo/Ni ratio of 0.1) shifts the reaction further to methanation selective with ∼100% CH4 selectivity as MoOx aids in the activation of both CO2 and CO. In contrast, the addition of a large amount of Mo (Mo/Ni ratio of 1) shifts the reaction to RWGS selective with a CO selectivity > 94%. This is attributed to the enhanced CO desorption from the surface as a result of MoOx modification.

Ruoyu Zhang

Papers

Tuning reverse water gas shift and methanation reactions during CO2 reduction on Ni catalysts via surface modification by MoOx