Hydrogenolysis of methyl heptanoate over Co based catalysts: Mediation of support property on activity and product distribution

Abstract

Co/MgO, Co/SiO2 and Co/Hβ catalysts were prepared by incipient wetness impregnation. The formation of MgO-CoO solid solution and MgCo2O4 spinel in Co/MgO resulted in high dispersions of Co on MgO even at the low calcined temperatures and the high Co loadings. The second impregnation of Co on Co/MgO enhanced Co cations in surface/subsurface of catalysts, which led to the enlarged metallic Co particle sizes by H2 reduction. Comparatively, the highly dispersion of Co was only observed on SiO2 and Hβ at the low Co loadings owing to the Coδ+ species of strong interactions with these supports. The solid solution/spinel and the strongly interacted Coδ+ species induced the Co cations reduced at higher temperatures with obtaining the small Co particle sizes. These cases also significantly decreased the basicities of Co/MgO depending on calcined temperature and Co loadings, and increased the acidic sites of Co/SiO2 and Co/Hβ with obtaining enhanced acidities, respectively. During hydrogenolysis processing, the basic sites of Co/MgO triggers the splitting of acyl CO bond of methyl heptanoate to form heptanal and methanol, followed by further hydrogenation of heptanal to 1-heptanol. While the acidic Co/SiO2 and Co/Hβ induce the cracking of ether CO bond to heptanoic acid and CH4. Heptanoic acid intermediate is then converted into C6 and C7 alkanes by the parallel decarbonylation and HDO pathways, respectively. The activity and product distribution could be facilely mediated by the synergistic catalysis of metal and acid/base. Under optimal conditions, the maximal 1-heptanol and summed C6/C7 alkanes yields of 55% and 89% were observed over Co/MgO and Co/SiO2 with desire Co loadings, respectively, indicating the promising applications of these catalysts in hydrogenolysis of vegetable oils.