The Role of Boron Sites in Side-chain Alkylation of Toluene with Methanol and a High Performance Composite Catalyst
Side-chain alkylation of toluene with methanol attracts interest for decades as a one-step alternative pathway to manufacture styrene under mild conditions. And a high performance catalyst is the most urgent need for realizing commercial application of this technology. Herein, we studied the role of boron sites in improving the styrene/ethylbenzene ratio (ST/EB) in side-chain alkylation products primarily. It was found that there was a synergistic catalysis effect between the boron sites and the cesium ion exchanged zeolite X (CsX), and this synergistic catalysis effect mainly accounts for the inhibition of further conversion of styrene to ethylbenzene in the side-chain alkylation products. Moreover, it was found that the synergistic catalysis effect could be influenced tremendously by the distance between the boron sites and the base sites of CsX and introducing boron sites by mixing boric acid impregnated SiO2 (B/SiO2) with CsX by grinding was an efficient way to greatly improve the ST/EB in the side-chain alkylation products. Finally, based on above findings, a ternary composite catalyst with high yield of side-chain alkylation products (styrene and ethylbenzene) and high ST/EB, which were 39.45% and 1.81 respectively, was developed by mixing CsX, cesium oxide modified CsX and B/SiO2 with the grinding route. What’s more, the key points for preparing a more efficient catalyst for side-chain alkylation of toluene with methanol in the future was also discussed and proposed.