Highly active Cu-Zn-Mg-Al-O catalyst derived from layered double hydroxides (LDHs) precursor for selective hydrogenolysis of glycerol to 1,2-propanediol

Abstract

Selective hydrogenolysis of glycerol to 1,2-propanediol (1,2-PDO) was performed by using environmentally friendly bifunctional layered double hydroxide (LDHs) type Cu-Mg-Al-O and Cu-Zn-Mg-Al-O catalysts prepared by urea hydrolysis method. The physicochemical properties of these catalysts were characterized by various techniques such as specific surface area (BET), X-ray Diffraction (XRD), H2-temperature programmed reduction (TPR) and scanning electron microscopy (SEM) etc. Ball-flower shaped particles were identified in SEM images of all the catalysts and a well-defined layered structure of solid lamella has also been identified. The SEM images confirmed the formation and stability of LDHs type structure of the catalysts even after calcination and reduction. The catalytic activity results depicted that, very high catalytic activity (>80%) with very high selectivity (>90%) to 1,2-PDO was obtained over all the catalyst synthesized. However, among all other, Cu-Zn-Mg-Al-O catalyst was the most active and selective to 1,2-PDO. The synergic interaction between the copper and ZnO on LDHs support, high reducibility, small Cu particle size and well-developed curved platelet structure were solely responsible for better catalytic activity of Cu-Zn-Mg-Al-O catalyst as compared to Cu-Mg-Al-O catalyst. The maximum glycerol conversion of 98.4% with 94.3% selectivity to 1,2-PDO was achieved over Cu-Zn-Mg-Al-O catalyst at optimum reaction condition i,e. at 210°C, at 4.5MPa pressure after 12h of reaction in presence of 1g of NaOH as additive. The selectivity (>94%) to 1,2-PDO was almost unchanged even after cycle-3 although the activity was reduced significantly.