(560fb) An Effective Microkinetic Modelling Strategy for Direct DME Synthesis from Syngas over Hybrid Cza/FER Catalyst

In this study, an effective microkinetic model approach was applied to direct synthesis of dimethyl ether (DME) from syngas over Cu-ZnO-Al₂O₃/FER (CZA/FER) which is a hybrid bifunctional catalyst consisting of CZA and ferrierite (FER). The possible reaction network for syngas to methanol reaction suggested by Grabow and Mavrikakis¹, composed of CO and CO₂ hydrogenations, and water-gas shift (WGS) reactions was considered, and both associative and dissociative pathways were included for methanol to DME reaction. In particular, the reaction energetics for methanol to DME reaction were calculated based on Møller-Plesset (MP) perturbation theory which is one of quantum chemistry post-Hatree-Fock ab initio methods in order to consider dispersion forces occurring in the reaction system. Meanwhile, pre-exponential factors to be fitted to experimental data were selected on the basis of sensitivity analysis, reducing the computational load without calculating the partition functions of translational, vibrational and rotational modes. Based on relative reaction rates, the most likely reaction pathways were searched out with the parameter-fitted model, and the rate-limiting step was suggested by calculating the degree of rate control. Also, appropriate operating conditions were proposed considering the effects of pressure, temperature and feed composition on DME synthesis rate. Conclusively, the effectively developed microkinetic model could be utilized to obtain valuable information on the reaction mechanisms, kinetics and optimal operating conditions for direct synthesis of DME from syngas over the hybrid catalyst.

REFERENCE

1. Mavrikakis M, Grabow LC. Mechanism of methanol synthesis on Cu through CO₂ and CO hydrogenation. ACS Catal. 2011;1:365-384.