Vapor-phase hydrodeoxygenation of guaiacol for phenol production using bifunctional Ni/Cu-Beta zeolite catalysts

Abstract

A series of bifunctional catalysts based on beta zeolite were prepared though co-impregnation and tested for vapor-phase hydrodeoxygenation (VHDO) reaction to form phenol. Among the catalysts tested, 10Ni/Cu-Beta exhibited the highest stability, catalytic activity, and selectivity for phenol. Under the optimal conditions of a contact time (W/F) of 1.5 h, a molar flow of hydrogen to guaiacol (H/G) of 24, a time of stream (TOS) of 40min. A temperature of 450 °C, and a molar flow of stream to guaiacol (S/G) of 3, complete conversion was achieved, with a phenol yield of 63.95% and a sum yield of phenolic compounds of 96.89%. The beta zeolite support provided an adequate specific surface area and initial acid sites for the VHDO process. In the absence of water, the addition of Cu metal improved catalytic performance of the catalyst. However, the increase in temperature could result in more severe deactivation. The addition of water had little effect on the catalyst activity and helped to improve its stability to a certain extent. The loading of Ni metal contributed to an increased selectivity for phenol. The characterization results from X-ray diffraction (XRD) and hydrogen temperature-programed reduction (H2-TPR) showed that reduced and oxidized metals are finely dispersed on the catalyst surface. NH3 temperature-programed desorption and pyridine infrared resonance (Py-IR) characterizations revealed that the addition of Cu and Ni metal adjusts the type and amount of acid sites. A small part of Cu2+ and Ni2+ could be bound simultaneously to the surface of beta support, of which Cu2+ forms new metal-induced L-sites while Ni2+ does not, resulting in a lower concentration of L-sites on Ni/Cu-based catalysts compared to that on Cu-based catalysts and weakening the transmethylation reaction of phenolic compounds. The combination of metal sites and acid sites enabled the VHDO reaction of guaiacol to produce more phenol in the products.