Steam reforming of acetic acid over nickel catalysts: Impacts of fourteen additives on the catalytic behaviors

This study investigated the effects of a series of additives ranging from alkali, alkali earth, transition and rare earth metals (Na, Mg, K, Ca, Sc, Cr, Mn, Fe, Co, Cu, Zn, Zr, La, Ce) on catalytic behaviors of Ni/Al2O3 in steam reforming of acetic acid. The addition of alkali and alkaline metals led to the sintering of alumina and nickel species. Cr, Ce or Zr addition filled pores, while Mn addition enhanced the specific area by creating more pores. Cu and Zn addition probably led to merging of small pores. In addition, K or Na promoted reduction of nickel oxides, promoting the catalytic activity. La, Ce or Co also enhanced activity of the catalysts, while Mg, Ca, Sc, Cu, Zn or Zr decreased the activities. The K or Na modified catalysts was much more stable than that of the La or Ce modified catalysts, although the coking was more serious. The coke formed in K or Na modified catalysts was mainly in fibrous form (probably the catalytic coke), while that in La or Ce modified catalysts was mainly amorphous form (probably the polymeric coke). The fibrous coke did not lead to the fast deactivation of the nickel catalysts as the amorphous coke did. The TG-MS and DRIFTS study showed that the coke contained the aliphatic structures with the functionalities such as methyl group, carbonyl groups, carboxylic structures as well as the structures of aromatic rings. The amorphous coke formed in La or Ce modified catalysts contained more aliphatic structures. The in situ DRIFTS study of steam reforming of acetic acid showed that a number of reaction intermediates including the -OH, C=O, aliphatic C=C, aromatic C=C, COO,=C-H, -CH3, aliphatic C-O-C structure, and absorbed CO2 involved in the reforming reaction. (C) 2019 Energy Institute. Published by Elsevier Ltd. All rights reserved.