Surface-silanised and alkoxylated micro-mesoporous Ni/hierarchical nanozeolites for oleic acid hydrodeoxygenation

In this work, we report a novel and green method for the synthesis of hierarchical nanozeolites for the hydrodeoxygenation of oleic acid to diesel-range hydrocarbons. Hierarchical nanozeolites based on HZSM-5 and HBEA with appropriate mesopores (8–20 nm) were synthesised through the surface silanisation of zeolitic seeds. In this method, organosilane (hexadecyltrimethoxysilane) was used as a growth inhibitor while biomass-derived alcohols (1-decanol and isobutanol) were used to improve the miscibility and dispersion of the organosilane. 1H MAS NMR analysis confirmed the silanisation and alkoxylation of the zeolitic seeds. The physicochemical properties of the catalysts were analysed by XRD, N2 porosimetry, NH3-TPD, pyridine-DRIFTS, XPS and TEM, and the catalytic performance of bifunctional 10 wt.% Ni/h-HZSM-5 and Ni/h-HBEA were then evaluated in the HDO of a bulky feedstock, oleic acid. The hierarchical zeolites supported Ni catalysts achieved more than 86% conversion of oleic acid. Compared with their microporous nanozeolite counterparts, Ni/h-HBEA and Ni/h-HZSM-5 exhibited comparable or higher Brønsted/Lewis acid ratios, leading to high selectivity towards C18 alkanes (65% and 71%, respectively); they also demonstrated similar catalytic yields. More importantly, while their microporous analogues lost much of their activity after the first cycle, Ni/h-HZSM-5, in particular, displayed excellent stability, even after four cycles. Thus, our approach appears to be a promising way of preparing catalyst supports for efficient hydrotreatment of bulky substrates.