The role of nanosized zeolite Y in the H2-free catalytic deoxygenation of triolein

Abstract

H₂-Free catalytic deoxygenation of biomass-derived organic compounds is an important technology to produce green hydrocarbons without the relevant carbon footprint associated with H₂. In this work, the effects of the crystal size of zeolite Y (Y20: 20 nm, Y65: 65 nm, Y380: 380 nm and Y2750: 2.75 μm) on the deoxygenation reaction of triolein are reported. The reaction is performed under solvent-free conditions without the addition of hydrogen. As the crystal size decreases, the triolein conversion and the yield of deoxygenated products increase. In addition, better product quality is obtained: higher hydrocarbon formation, higher diesel formation, lower formation of heavy hydrocarbons and higher diesel-to-gasoline ratio are observed. The high activity is related to the high concentration of acid sites, with accessible medium acid strength comprised of Brønsted and Lewis acid sites located on the external surface of the crystals. A linear relationship is observed between the rate constant of triolein depletion and the amount of medium strength acid sites. Further conversion of the fatty acids which are obtained from the hydrogenolysis of triolein (first rate-determining step) to deoxygenated products occurs on the surfaces of the zeolite crystals. The better accessibility of the Y20 sample with the smallest crystal size leads to improved catalytic performance. In comparison with previously reported catalysts, H₂-free deoxygenation over nanosized zeolite Y appears to be an interesting industrial option to obtain high yields of green diesel.