High CO conversion in syngas to aromatics by addition of ZnMnZr oxides as methanol synthesis components

Abstract

In the oxide-zeolite (OX-ZEO) strategy, it is challenging to achieve both higher CO conversion and aromatics selectivity. In this paper, the methanol synthesis component xZn2Mn8Zr was prepared. With increasing Zn content, CO conversion over the ternary oxides increased without a remarkable decrease in the combined selectivity of methanol and dimethyl ester (DME). The 2Zn2Mn8Zr (molar ratio) was then coupled with either SAPO-34 or H-ZSM-5 for syngas conversion. Combined with the results of thermogravimetric analysis, a bifunctional catalyst with more residual hydrocarbon pool species (HCPs) was capable of achieving higher selectivity of unsaturated organic products. The loss of HCPs should be attributed to over-hydrogenation. The over-hydrogenation could be related to either Zn concentration or the close contact of 2Zn2Mn8Zr with H-ZSM-5. To alleviate such over-hydrogenation, ZnMnZr pellets with lower Zn concentration were mixed with the pellets of 6Mn4Zr/H-ZSM-5 using a granule mixing method. The multi-functional catalyst exhibited much higher activity in syngas-to-aromatics (STA) conversion, especially at high space velocities. The CO conversion over the multi-functional catalyst could reach 43% at 600 mL g_cat⁻¹ h⁻¹, with aromatics selectivity around 72%, and it remained stable during a 100 h reaction.