Thermodynamic and Mechanistic Analyses of Direct CO Methylation with Toluene to -Xylene.

Direct CO methylation with toluene, as one of the CO hydrogenation technologies, exhibits great potential for the CO utilization to produce the valuable -xylene (PX), but the tandem catalysis remains a challenge for low conversion and selectivity due to the competitive side reactions. The thermodynamic analyses and the comparation with two series of catalytic results of direct CO methylation are conducted to investigate the product distribution and possible mechanism in adjusting the feasibility of higher conversion and selectivity. Based on the Gibbs energy minimization method, the optimal thermodynamic conditions for direct CO methylation are 360-420 °C, 3 MPa with middle CO/CH ratio (1:1 to 1:4) and high H feed (CO/H = 1:3 to 1:6).