Effect of Metal Active Sites on the Product Distribution over Composite Catalysts in the Direct Synthesis of Aromatics from Syngas

The conversion of syngas to aromatics over composite catalysts, comprising a mixture of Fe 2 O 3 -SiO 2 and Nb-/Ni- modified HZSM-5 (HZ), CuO-ZnO-Al 2 O 3 (CZA) and Nb-/Ni- modified HZ, and a mixture of above two kinds of metal oxides and Ni-HZ, were investigated at 330 °C, 4 MPa and H 2:CO = 2:1. Catalysts were characterized to analyze the properties. Fe 2 O 3 -SiO 2 /modified-HZ had the high selectivity of BTX, while CuO-ZnO-Al 2 O 3 /modified-HZ had the high selectivity of durene. Fe-CZA/Ni-HZ exhibited higher selectivity of trimethylbenzene (triMB) than both Fe/Ni-HZ and CZA/Ni-HZ, lower selectivity of BTX and tetramethylbenzene (tetraMB), compared with Fe/Ni-HZ and CZA/Ni-HZ, respectively. Reaction pathways were speculated to illustrate the diverse distribution of aromatics. The incorporation of Nb and Ni on the parent HZSM-5 increased the selectivity of aromatics due to their various acidity. The highest selectivity of BTX was obtained over Fe/Ni-HZ and the highest selectivity of durene was achieved over CZA/Nb-Ni-HZ.