Applied Catalysis B: Environmental, Vol.250, 280-291, 2019
Enhanced direct deoxygenation of anisole to benzene on SiO2-supported NiGa alloy and intermetallic compound
Herein, Ni/SiO2 and bimetallic Ni.Ga/SiO2 (Ni/Ga atomic ratio x = 6 and 3) catalysts were prepared by the impregnation method followed by reduction at 550 degrees C and tested in the vapor hydrodeoxygenation of anisole at 0.1 MPa and 300 degrees C. Ni-Ga alloy and Ni3Ga intermetallic compound (IMC) formed in Ni6Ga/SiO2 and Ni3Ga/SiO2, respectively, where the Ga atoms break contiguous Ni ones reducing the ensembles of Ni atoms and the H-2 uptakes. Also, a charge transfer from Ga to Ni increased the electron density of Ni, and hydrogen spill-over occurred on NixGa/SiO2. In contrast to Ni/SiO2, Ni Ga/SiO2 improved not only the hydrodeoxygenation activity but also the selectivity to benzene. At the similar anisole conversion C31%), the selectivity to benzene was 75.2%, 83.0% and 92.6% on Ni/SiO2, Ni6Ga/SiO2 and Ni3Ga/SiO2, respectively. Reactivity evaluation, anisole-TPD and TPSR results show that the direct CAr OCH3 bond cleavage (C-Ar represents the carbon in benzene ring) to benzene was more preferential on Ni Ga/SiO2 than on Ni/SiO2. Isotope tracing experiment indicates that the spilt-over hydrogen at the interface between the Ni3Ga particles and support participated in the reaction. We suggest that the synergetic effect between Ni and Ga facilitated the direct C-Ar-O bond cleavage. Moreover, NixGa/SiO2 were less active for benzene hydrogenation and C-C bond hydrogenolysis than Ni/SiO2, contributing to higher selectivity to benzene. Significantly, methanol, derived from the direct the CA,. OCH3 bond cleavage, dominatingly decomposed to CO and H-2 and methanation scarcely occurred on Ni Ga/SiO2, however, it was mainly converted to methane on Ni/SiO2. Low activities for benzene hydrogenation, C C bond hydrogenolysis and methanation on NixGa/SiO2 (especially Ni3Ga/SiO2) are attributed to the geometric and electronic effects of Ga in alloy and IMC. The finding is significant in rationally designing the catalyst with high benzene yield and low H-2 consumption.