Tuning the CO₂ Hydrogenation Activity and Selectivity by Highly Dispersed Ni–In Intermetallic Alloy Compounds

Abstract

Reverse water−gas shift (RWGS) reaction is considered as an effective solution for conversion of greenhouse gas of the CO 2 to CO, but it still suffers from relatively low activity and selectivity at low temperatures. Herein, we report the catalytic performance and mechanism of NiIn x /SBA-15 with different Ni and In (indium) molar ratios for the RWGS reaction at a low temperature. The results showed that the increment of the In/Ni ratio in intermetallic alloy compounds (IMCs) inhibits CO* adsorption through the "active site isolation" effect, thus improving selectivity of CO. In terms of In−Ni IMCs, Ni acts as the active center but is isolated by In atoms for the CO 2 hydrogenation reaction. XRD and HRTEM showed that Ni and In formed the IMC and were highly dispersed on the large surface area of SBA-15. It was also demonstrated by H 2 -TPR that the addition of In enhanced the interaction between Ni and the support, thus improving the stability of the catalyst with good anti-sintering. Meanwhile, the aggregation charge density of Ni was obtained by In additives, as verified by XPS and DFT simulation. After optimizing the In/Ni molar ratio, the NiIn 0.5 /SBA-15 exhibited a CO 2 conversion of 29% at 400 °C, 0.1 MPa, and 24,000 mL/g cat •h, with a CO selectivity of over 99% and a production rate of about 47 mmol/g cat •h, which is superior to those of the most reported nickel-based catalysts. At the same time, NiIn 0.5 /SBA-15 showed good long-time stability and the conversion of CO 2 was maintained well after a 25 h reaction. In situ DRIFTS reveals a change for surface intermediates from HCOO* to COOH* during CO 2 activation after the introduction of In, leading to a rapid desorption of CO and avoiding further hydrogenation to form CH 4 , which can also be demonstrated by CO-TPD. The highly dispersed Ni−In IMCs with weak adsorption capacity of CO are the main reason for achieving high activity and selectivity for RWGS at low temperatures.

Multivariate Bayesian Optimization of CoO Nanoparticles for CO2 Hydrogenation Catalysis

“…The selective hydrogenation of CO 2 to value-added chemicals and fuels not only reduces our dependence on nonrenewable resources but also has the added benefit of utilizing waste CO 2 instead of emitting it to the atmosphere. − A variety of catalysts for thermocatlytic CO 2 hydrogenation including metals, , intermetallic compounds, , and metal oxides − have been developed for reverse water gas shift, methanol synthesis, methanation, and C–C coupling reactions to yield long-chain alkanes and higher alcohols. − One highly studied class of materials for CO 2 hydrogenation catalysis is transition metal oxides. Among these, cobalt oxide is a transition metal oxide of interest because of its versatility across a broad range of catalytic transformations, including electrochemical water splitting, CO oxidation, and nitric oxide reduction, as well as CO 2 hydrogenation. − However, the complexity of cobalt oxide-based catalysts, which can include multiple valence states (e.g., Co 2+ and Co 3+ ) and crystal structures, coupled with the variety of transformations they can promote, has led to challenges in understanding and tailoring robust and selective catalysts. − Two of the most thermodynamically stable phases of cobalt oxide are CoO, which has the rock salt structure type, and Co 3 O 4 , which has the spinel structure type.…”