Catalytic Alkylation of 2,6-Xylenol with Methanol to Alkylphenols Over H-Composite Zeolite Supported Palladium Nanoparticles

Abstract

Development of catalytic alkylation to produce alkylphenols with simple and high-yield components is an effective strategy for value added utilization of crude phenols. Herein, the H-composite zeolite (HCZ) supported palladium nanoparticles (Pd NPs) catalysts was studied in 2,6-xylenol alkylation with methanol, followed the exploring alkylation mechanism by investigating the synergistic effects between accessible acid sites and Pd centers to enhance the Lewis acidic sites. As-prepared catalyst (Pd@HCZ) was characterized by multiple technological strategies, such as XRD, XPS, N2-adsorption, FE-SEM, TEM, NH3-TPD, and in situ infrared to investigate it structural and physicochemical properties. As a demonstration, Pd@HCZ has an extraordinarily 2,6-xylenol conversion and alkylphenols yield (100% and 97.5%), respectively, compared to the Pd@HY (63.8% and 53.1%), and Pd@Hβ (65.0% and 64.8%) at 240 oC for 4 h under atmospheric conditions. Correspondingly, first principle calculations reveal that high catalytic alkylation activity originate from synergistic effects between Pd centers and accessible Lewis acidic sites to enhance the ability of phenolic OH group adsorption methanol or/and dimethyl ether over Pd@HCZ. In addition, the pure alkylphenol products were obtained after further alkylation reaction and elution by their structures, which can improve the industrial application value of crude phenols under mild conditions.

Keywords: Catalytic alkylation, Alkylphenols, Pd@HCZ, Synergistic effects, Mechanisms