Acid properties of the hybrid catalyst CuO–ZnO or CuO–ZnO–Al2O3/H-ferrierite: An infrared study

The acid properties of hybrid catalysts based on CuO–ZnO or CuO–ZnO–Al2O3 supported on the H-ferrierite zeolite were studied by NH3-TPD and FTIR using two molecular probes, pyridine and d3-acetonitrile. The samples were prepared using two different methods. The acid strength of these hybrid catalysts was considerably reduced by decreasing the amount of zeolite, and by the partial blockade of the acid sites by the CuO–ZnO or CuO–ZnO–Al2O3 component. However, strong acid sites still remained in the catalyst prepared by coprecipitation–sedimentation. Highly dispersed phases of Cu, Zn, and Al oxides promoted a minor blockage of the zeolite acid sites. Pyridine has been shown to be a suitable molecular probe to identify the Bronsted and Lewis acid sites in the hybrid catalysts. More Lewis acid sites were formed, and a high reduction in Bronsted acid sites was observed in all samples compared to H-ferrierite zeolite. Infrared spectra of adsorbed d3-acetonitrile for the hybrid catalysts varied according to the method used for preparation. Interaction between Si–OH and d3-acetonitrile was observed only for the samples prepared by coprecipitation–impregnation. With acetonitrile, strong Lewis acid sites were observed in all samples, and band intensity was proportional to the amount of zeolite. Bronsted acid sites were only observed in samples prepared by coprecipitation–sedimentation.