Preparation and Catalytic Performance of Ni/γ-Al2O3 Catalysts for the Reverse Water–Gas Shift Reaction

Selective CO2 hydrogenation over Ni-based catalysts requires control of the competing reverse water–gas shift (RWGS) and methanation pathways. Here, γ-Al2O3-supported Ni catalysts with nominal loadings of 5, 10, 15 and 20 wt% were prepared by wet impregnation. Structural, textural, reduction and surface analyses showed that Ni loading altered NiO crystallinity, pore accessibility, reducibility and the fitted surface Ni-state distribution. The 10%Ni/γ-Al2O3 catalyst reached 55% CO2 conversion, approximately 90% CO selectivity and a CO production rate of 147.2 mmol CO·gcat−1·h−1 at 600 °C. Increasing the H2/CO2 ratio from 1 to 4 at 500 °C raised conversion from 46% to 65% but decreased CO selectivity from 88% to 76%. The catalyst also maintained a nearly constant response during a 24 h time-on-stream test at 500 °C. In situ DRIFTS detected bicarbonate-, formate- and adsorbed-CO-related species, consistent with the participation of oxygenated intermediates in RWGS. Together, these results establish an internally controlled loading–structure–performance relationship and identify 10%Ni/γ-Al2O3 as providing the most favorable conversion–selectivity–productivity balance within the investigated series.