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

Reverse water–gas shift (RWGS) reaction is considered as an effective solution for conversion of greenhouse gas of the CO2 to CO, but it still suffers from relatively low activity and selectivity at low temperatures. Herein, we report the catalytic performance and mechanism of NiInx/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 CO2 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 H2-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 NiIn0.5/SBA-15 exhibited a CO2 conversion of 29% at 400 °C, 0.1 MPa, and 24,000 mL/gcat·h, with a CO selectivity of over 99% and a production rate of about 47 mmol/gcat·h, which is superior to those of the most reported nickel-based catalysts. At the same time, NiIn0.5/SBA-15 showed good long-time stability and the conversion of CO2 was maintained well after a 25 h reaction. In situ DRIFTS reveals a change for surface intermediates from HCOO* to COOH* during CO2 activation after the introduction of In, leading to a rapid desorption of CO and avoiding further hydrogenation to form CH4, 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.