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

Co/MgO, Co/SiO2 and Co/H beta 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 H-2 reduction. Comparatively, the highly dispersion of Co was only observed on SiO2 and H beta at the low Co loadings owing to the Co delta+ species of strong interactions with these supports. The solid solution/spinel and the strongly interacted Co delta+ 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/H beta with obtaining enhanced acidities, respectively. During hydrogenolysis processing, the basic sites of Co/MgO triggers the splitting of acyl C-O 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/H beta induce the cracking of ether C-O bond to heptanoic acid and CH4. Heptanoic acid intermediate is then converted into C-6 and C-7 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 C-6/C-7 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. (C) 2013 Elsevier B.V. All rights reserved.