Key function mechanism of Na3PO4-modified NaX for enhanced performance and stability in side chain alkylation of toluene with methanol: DFT and experimental perspectives

Abstract

The balance of acid-base property is crucial for the catalytic performance of Side-Chain Alkylation of Toluene with Methanol (SATM). In this work, Na₃PO₄ modified NaX catalysts with suitable middle base strength and feasible acid-base center distance were prepared by direct solvent-evaporation and exhibited the best styrene selectivity of 45.4 % and the total yield of side chain alkylation products of 71.7 %, respectively at methanol conversion up to 99.9 % in NaX-P_(0.075). Notably, the selectivity exhibits surprising stability in the evaluated 15 days, which might owe to the uniform dispersion of active species and constant acid base property. Combined the comprehensive characterizations of solid-state NMR, FTIR, SEM, and XPS, etc., with Density Functional Theory (DFT) calculation results, it is revealed that O-1264 are affected mostly by loading Na⁺ or both of Na⁺ and PO₄^3-, which exhibits the least adsorption energy and the highest electronic cloud density in the four kinds of oxygen atoms according to the calculated Bader charge. Therefore, the structure S4 (O-1264) was considered to be the most stable and meet the basicity requirements for SATM.