Manganese Oxide as a Promoter for Copper Catalysts in CO(2) and CO Hydrogenation

In this work, we discuss the role of manganese oxide as a promoter in Cu catalysts supported on graphitic carbon during hydrogenation of CO(2) and CO. MnO(x) is a selectivity modifier in an H(2)/CO(2) feed and is a highly effective activity promoter in an H(2)/CO feed. Interestingly, the presence of MnO(x) suppresses the methanol formation from CO(2) (TOF of 0.7 ⋅ 10(−3) s(−1) at 533 K and 40 bar) and enhances the low‐temperature reverse water‐gas shift reaction (TOF of 5.7 ⋅ 10(−3) s(−1)) with a selectivity to CO of 87 %(C). Using time‐resolved XAS at high temperatures and pressures, we find significant absorption of CO(2) to the MnO, which is reversed if CO(2) is removed from the feed. This work reveals fundamental differences in the promoting effect of MnO(x) and ZnO(x) and contributes to a better understanding of the role of reducible oxide promoters in Cu‐based hydrogenation catalysts.