Direct synthesis of dimethyl ether on the admixed nanocatalystsof CuO–ZnO–Al2O3 and HNO3-modified clinoptilolite at high pressures: Surface properties and catalytic performance

The potential of clinoptilolite as a methanol dehydration catalyst in direct conversion of syngas to dimethyl ether has been investigated. The modified form of clinoptilolite was obtained by nitric acid treatment. Although the physicochemical analysis showed that crystallinity of the clinoptilolite decreased during HNO3-treatment, the specific surface area of natural zeolite increased considerably. Size distribution histogram of the synthesized nanocatalyst showed that the particle size of active phase was between 28.9 and 112.9 nm with an average size of 53.9 nm. The NH3-TPD profiles showed that both the number and strength of the acid sites of the CuO–ZnO–Al2O3/clinoptilolite nanocatalysts decreased with increasing active phase content. Results indicated that the optimal reaction temperature and pressure for this nanocatalysts were 300 °C and 40 bar, respectively. The catalytic performance of synthesized samples showed that the optimum CuO–ZnO–Al2O3 to clinoptilolite ratio was 4:1, which depends on temperature and pressure.