Direct synthesis of dimethyl ether as a green fuel from syngas over nanostructured CuO–ZnO–Al2O3/HZSM-5 catalyst: Influence of irradiation time on nanocatalyst properties and catalytic performance

•Synthesis of CuO–ZnO–Al2O3/HZSM-5 by ultrasound assisted co-precipitation method.•Significant changes in nanocatalyst morphology after ultrasound irradiations.•Smaller particle aggregates with better dispersion in longer irradiated catalysts.•Improvement in reactivity and stability of the longer ultrasound irradiated nanocatalyst.

CuO–ZnO–Al2O3/HZSM-5 (CZAZ) nanocatalyst is prepared by ultrasound-assisted co-precipitation method at different irradiation times, characterized and tested for direct synthesis of DME from syngas. Synthesized nanocatalysts were characterized using XRD, FESEM, PDS, EDX and BET techniques. Direct synthesis of DME is carried out at 200–300 °C and 10–40 bar using a mixture of CO:H2 = 2:1. The catalyst with the longest sonication time showed the smallest degree of aggregates, the highest dispersion and surface area. Although the long irradiated nanocatalyst has slightly bigger CuO crystal size but the size of particle aggregates was small and less populated. The sonicated catalyst with longest irradiation presented a high CO conversion of ca. 40%. It seems that, not the CuO crystal size but the size of particle aggregates and nanocatalyst surface had a great effect on the CZAZ nanocatalyst performance. While there was an optimal temperature for CO conversion and DME yield in direct synthesis of DME, both the CO conversion and the DME yield increased with the pressure increase. Long irradiated nanocatalyst yielded more stable CuO–ZnO–Al2O3/HZSM-5 nanocatalyst while conventional co-precipitated nanocatalyst lost its activity ca. 11% and 58% in terms of CO conversion and DME yield, respectively, in 24 h time on stream test.

Graphical abstractCuO–ZnO–Al2O3/HZSM-5 nanocatalyst has been prepared by ultrasound-assisted co-precipitation method, characterized and tested for direct synthesis of DME from syngas (STD). Among sonicated nanocatalysts, the one with the longest irradiation time show better dispersion, aggregate free morphology and the highest surface area. The longest irradiated nanocatalyst presented the best activity and CO conversion of ca. 40%. Testing operational conditions exhibited, while there was an optimal temperature for CO conversion and DME yield in direct synthesis of DME, CO conversion and DME yield both increased with the pressure increase. Furthermore long irradiated nanocatalyst yielded more stable CuO–ZnO–Al2O3/HZSM-5 nanocatalyst while conventional co-precipitated nanocatalyst lost their activity ca. 11% and 58% in terms of CO conversion and DME yield respectively in 24 h time on stream test.Figure optionsDownload full-size imageDownload as PowerPoint slide