The hierarchical effects of zeolite composites in catalysis

A series of zeolite composites with hierarchically porous structures and tunable acidities were prepared. The structural, crystalline, and textural properties of the as-synthesized materials, as well as the reference Y and β zeolite samples, were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)/transmission electron microscopy (TEM) analyses, Fourier transform infrared spectroscopy (FTIR), and nitrogen adsorption/desorption techniques. The acidic properties of the surface were determined by in situ FTIR of adsorbed pyridine. The hierarchy factor is an appropriate tool to classify hierarchically structured materials, and the hierarchical pores of the as-synthesized zeolite composite samples were investigated during the catalytic cracking of isopropylbenzene. The results show that the catalytic activity of isopropylbenzene cracking over the catalysts has a linear dependence with their hierarchy factor (HF). The tunable acidities were tested by methanol dehydration to dimethyl ether (DME), and the dehydration activity of methanol over the catalysts shows a linear decrease with the increased Lewis/Brönsted ratio, while the selectivity of DME shows a linear increase with the enhanced Lewis/Brönsted ratio.