Direct syngas to DME as a clean fuel: The beneficial use of ultrasound for the preparation of CuO–ZnO–Al2O3/HZSM-5 nanocatalyst

A series of CuO–ZnO–Al₂O₃/HZSM-5 nanocatalysts prepared by impregnation, co-precipitation–physically mixing and combined co-precipitation–ultrasound methods and their catalytic activity investigated toward direct conversion of syngas to DME. BET, XRD, FESEM, TPR-H₂ and FTIR techniques were used to characterize nanocatalysts. XRD and FTIR results showed that structure of HZSM-5 is not damaged even after it is loaded with CuO–ZnO–Al₂O₃ nanoparticles. TPR-H₂ profiles indicated that reducibility of co-precipitation–ultrasound nanocatalyst is higher than other catalysts. It is found that employing ultrasound energy has great influence on the dispersion of nanocatalyst and its catalytic performance. Size distribution histogram of this nanocatalyst indicated that active phase particle size is between 25.7 and 125.4 nm and their average size is 47.86 nm. The physically mixing of CuO–ZnO–Al₂O₃ and HZSM-5 resulted in the low catalytic activity, indicating that the closest packing of both active sites for CO hydrogenation and methanol dehydration is necessary for direct synthesis of DME. The nanocatalyst loses negligible activity over the course of reaction due to coke formation on copper species.     

Influence of ambient gas on microwave-assisted combustion synthesis of CuO–ZnO–Al2O3 nanocatalyst used in fuel cell grade hydrogen production via methanol steam reforming

The effect of different ambient gases for preparation of CuO-ZnO-Al₂O₃ nanocatalysts by the microwave assisted solution combustion method was studied. Air, nitrogen and carbon dioxide as the ambient atmospheres were injected during the solution combustion synthesis method. The fabricated nanocatalysts were characterized by various techniques such as XRD, FESEM, TEM, EDX, FTIR and BET analyses. It was understood that injection of nitrogen during synthesis of nanocatalysts led to high dispersion of Cu crystallites as the active sites for the steam methanol reforming reaction. Moreover, appropriate interaction between CuO and ZnO particles was achieved due to better morphology of the nanocatalyst synthesized by N₂ as the ambient gas than other samples. Finally, high methanol conversion with proper products selectivity were achieved by the nanocatalyst synthesized by injection of N₂ during the microwave assisted combustion synthesis method due to significant superiority in its physicochemical properties.     

Low-temperature synthesis of DME from CO2/H2 over Pd-modified CuO–ZnO–Al2O3–ZrO2/HZSM-5 catalysts

Three series of Pd-modified CuO–ZnO–Al₂O₃–ZrO₂/HZSM-5 catalysts were prepared and characterized by BET, XRD and TPR analysis. The catalytic system was evaluated in the development of direct synthesis of dimethyl ether (DME) from carbon dioxide hydrogenation at low temperature (T=200 °C, P=3.0 MPa). The results indicated that the addition of palladium markedly enhanced the DME synthesis and retarded the CO formation. An explanation of this promoting effect of Pd on the DME synthesis could be attributed to the spillover of hydrogen from Pd⁰ to the neighboring phase.