Magnesia modified H-ZSM-5 as an efficient acidic catalyst for steam reforming of dimethyl ether

To develop an efficient acidic catalyst for steam reforming of dimethyl ether (DME), H-ZSM-5 was modified with a series amount of MgO (0–8.16 wt.%) via the incipient impregnation method by using Mg(NO3)2 as a precursor. Irrespective of the MgO loadings studied, it was highly dispersed over H-ZSM-5, and very limited impact on the structure and crystallinity of the zeolite was unambiguously revealed by the techniques of XRD, FT-IR, and N2 adsorption at low temperatures. On the contrary, significant effects of MgO on the acidity of H-ZSM-5, especially the stronger acidic sites, were clearly manifested from the temperature-programmed desorption of ammonia (NH3-TPD). The amount of the stronger acidic sites was sharply decreased after loading 0.61 wt.% MgO on H-ZSM-5, and it was continuously decreased when the MgO loading was further increased until 8.16 wt.%. In contrast, the maximum amount of weaker acidic sites was observed between 1.41 and 2.92 wt.% MgO loaded samples. The MgO-modified H-ZSM-5 physically mixed with a commercial Cu/ZnO/Al2O3 was investigated as a bifunctional catalyst for steam reforming of DME (SRD). The reaction was performed in a fixed-bed reactor under the conditions of T = 290 °C, P = 1 atm, and GHSV = 4000 h−1. SRD results indicate that the DME conversion, H2 yield, and selectivity of the carbon-containing products were strongly dependent on the MgO loadings over H-ZSM-5, and the highest H2 yield of about 93% was achieved over the bifunctional catalyst by using 1.98 wt.% MgO modified H-ZSM-5 as a solid acid. Together with the reaction and characterization results of the Mg2+-exchanged H-ZSM-5, the property of the stronger acidic sites over the MgO-modified H-ZSM-5 was revealed to be a crucial factor in determining the SRD performance of the bifunctional catalyst. The simple impregnation procedure and the high efficiency in versatile tailoring the acidity make MgO-modified H-ZSM-5 a practical, highly efficient, and promising solid acid for hydrogen production via SRD.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► H-ZSM-5 modified with MgO was investigated as an acidic catalyst for SRD. ► MgO highly dispersed on H-ZSM-5 deteriorated its stronger acidic sites. ► Sharply decreased selectivity of hydrocarbon byproducts over MgO modified H-ZSM-5. ► Over 90% H2 yield obtained over H-ZSM-5 modified with optimal amount of MgO.