Boosting the performance of Ni/Al2O3 for the reverse water gas shift reaction through formation of CuNi nanoalloys

Abstract

Ni supported on alumina is extensively employed as a catalyst for the reverse water gas shift reaction. However, the formation of inactive Ni aluminates and the high selectivity to methane affects the performance of these catalysts, especially at low reaction temperatures. In this study, Cu is employed as an effective enhancer of the catalytic performance, promoting the reducibility of Ni, and suppressing methane production through the formation of stable CuNi nanoalloys. The synergy between both metals suppresses consecutive hydrogenation, reaching conversions close to equilibrium and 100% selectivity to carbon monoxide. At 500 °C, the CO yield of the Cu₂₅Ni₇₅/Al₂O₃ catalyst was twice that of Ni/Al₂O₃, with only half the hydrogen consumption. The formation of CuNi nanoalloys was confirmed by HAADF STEM–EDS, without segregation in monometallic phases even after 30 h time on stream. Similarly, Cu₅₀Ni₅₀/Al₂O₃ remained alloyed after the reaction. However, the catalytic activity decreased due to sintering, in agreement with a higher Cu content. This effect was significantly more pronounced for Cu₇₅Ni₂₅/Al₂O₃ and Cu/Al₂O₃, with formation of large particles and consequent loss of active surface area.