Redispersion effects of citric acid on CoMo/gamma-Al2O3 hydrodesulfurization catalysts

摘要

Calcined CoMo/gamma-Al2O3 catalysts were modified by citric acid (CA) with different CA/Co ratios and the corresponding structure evolutions were systematically characterized. Then combined with HDS activity results, potential redispersion effects of CA were suggested: (i) weaken the MoO3-Al2O3 interaction via competitive interacting with the OH groups of alumina surface to realize the redispersion of Mo oxides; (ii) transform tetrahedral MoO42- or beta-CoMoO4 into octahedral polymolybdate species and promote bulk MoO3 to form well dispersed MoO3; (iii) remove the CoAl2O4-like species. These effects probably together promote the resulting sulfided catalysts with more type II CoMoS active sites, thus enhancing the HDS activity. (C) 2016 Elsevier B.V. All rights reserved.