Single-step synthesis of dimethyl ether from syngas on Al₂O ₃-modified CuO-ZnO-Al₂O₃/ferrierite catalysts: Effects of Al₂O₃ content

Single step synthesis of dimethyl ether (DME) from syngas on the bifunctional catalysts of CuO-ZnO-Al₂O₃ deposited on Al₂O₃-modified H-ferrierite was investigated to elucidate effects of Al₂O₃ modification of H-ferrierite in terms of CO conversion and DME yield. The enhanced catalytic activity was observed on the bifunctional catalysts at an optimum content of Al₂O₃ on H-ferrierite around 2.5-5 wt%. It is attributed to a higher dispersion of Al₂O₃ on H-ferrierite with an enhanced interaction of copper particles with Al₂O₃ modified H-ferrierite with a lower aggregation property by adjusting acidic sites and by increasing the dispersion of copper particles. The main role of Al₂O₃ on H-ferrierite is found to reduce strong acidic sites by depositing on the sites selectively, which resulted in showing a lower formation of byproducts. Both of copper surface area and amount of acidic sites are well correlated with an intrinsic activity (turn-over frequency; TOF), which revealed a structure-insensitive reaction character of a single-step synthesis of DME. The measurements of the dispersion of Al₂O₃ and copper particles with the number of acidic sites concomitantly were employed to verify the effects of Al₂O₃ modification of H-ferrierite though X-ray photoelectron spectroscopy, temperature-programmed methods and surface morphology characterizations.