HIGHLY-ACTIVE METHANOL DISSOCIATION CATALYSTS DERIVED FROM SUPPORTED MOLTEN-SALTS

Catalysts prepared by supporting molten CuCl-KCl or CuCl-ZnCl2-KCl on SiO2, Al2O3, or ZnSiO3 support have been used to promote methanol dissociation to predominantly CO and H-2 (Eyman et al., ref 1). The catalysts were prepared by common impregnation procedures and did not require pretreatment before use. A wide range of operating conditions was examined in continuous flow, fixed-bed reactor tests. Methanol conversion rates (mol of CH3OH/L of catalyst.h) were very high: up to 6300 at 400-degrees-C, and as high as 12 000 at 500-degrees-C. Outstanding catalyst longevity and thermal stability were also observed. Several generalizations concerning catalyst composition can be made. Catalyst activity at low reaction temperatures increases with decreasing salt fusion temperatures. Catalysts comprising salts which are stable toward reduction show the highest activity at high temperatures. Compared with CuCl-KCl/SiO2, catalysts containing nonacidic ZnO promoter generally had higher CO selectivity. Higher activity is achievable by switching to ZnSiO3 or Al2O3 support, or by adding ZnCl2 to the supported melt, but these measures also increase side reactions. Catalytic activity increased over time due to chemical transformation of the copper phase. One of the CuCl-KCl/SiO2 catalysts was examined before and after use by electron microscopy and X-ray powder diffraction (XRD). From these studies it is possible to conclude that copper is present in mixed oxidation states in the high-activity catalyst-metallic and copper(I) oxide. Particle size estimates for the copper phases, obtained from electron microscopy and XRD line-broadening, are compared. The ternary salt catalyst, CuCl-ZnCl2-KCl/SiO2, was also tested for CO + H-2 synthesis activity at 300-degrees-C. The organic products were C1-C-7 hydrocarbons. Total hydrocarbon yield as a function of carbon number was reasonably well described by the Anderson-Schulz-Flory model.