Direct Conversion of Syngas to DME over Nanocatalysts of CuO-ZnO-Al2O3 and HNO3 Modified Clinoptilolite

The potential of clinoptilolite as a methanol dehydration catalyst in direct syngas to dimethyl ether conversion has been investigated. The modified form of clinoptilolite was obtained by nitric acid treatment. In order to address the effect of various ratios of CuO-ZnO-Al2O3 to clinoptilolite on the catalytic performance of the hybrid catalyst, a series of CuO-ZnO-Al2O3/Clinoptilolite nanocatalysts with different active phase content were successfully synthesized via co-precipitation method. Although the physicochemical analysis showed that crystallinity of the clinoptilolite decreased during HNO3 treatment, the specific surface area of natural zeolite increased obviously. Furthermore, the FESEM analysis indicated that the morphology of the clinoptilolite changed from leaf-like to the needle-like pattern. The crystallite size of CuO has not been influenced significantly by the CuO-ZnO-Al2O3content, while relative crystallinity was dramatically changed. Moreover, with increasing of CuO-ZnO-Al2O3/Clinoptilolite ratio, the specific surface area decreased. Size distribution histogram of the synthesized nanocatalyst showed that the particle size of active phase is between 28.9-112.9 nm with an average size of 53.97 nm. The NH3-TPD spectrums showed that both the number and strength of the acid sites of the CuO-ZnO-Al2O3/Clinoptilolite nanocatalysts decreased with increasing active phase content. The influence of reaction temperature and pressure was investigated in detail. Results indicated that the optimal reaction temperature and pressure for this catalyst were 300ºC and 40 bar, respectively. The catalytic performance is shown the optimum value for the composition of CuO-ZnO-Al2O3/Clinoptilolite nanocatalysts has been 4:1, which could be depended on temperature and pressure.

کلیدواژه ها:

ZnO-CuO-Al2O3 ، Clinoptilolite ، Co-precipitation ، Syngas ، DME