Effect of Clay Binder on Sorption and Catalytic Properties of Zeolite Pellets

Abstract

Sorption of N 2 , O 2 , Ar, and CH 4 in zeolites X, Y, and mordenite in powder as well as pellets was studied using gas chromatography. Heats of sorption in pellets formed using clay as a binder increased by 34-78% for N 2 and 7-18% for CH 4 relative to the respective zeolite powder. Surface acidity of zeolites upon pelletization as measured by ammonia temperature-programmed desorption showed that high-strength acid sites completely disappear for both zeolite Y and mordenite when bound with bentonite and attapulgite. Decreases in weaker acid sites upon pelletization for mordenite and HY are 47-52% and 34%, respectively. Fourier transform infrared spectroscopy also showed a decrease in acidity upon pelletization of zeolite powders as observed from the reduction in the intensity of the peaks corresponding to acidic hydroxyl groups. Influence of the decrease in surface acidity upon pelletization was also observed from conversion values for alkylation of toluene with methanol in zeolite pellets. For example, reduction in total xylene formed was by 50%, 87%, and 100% for HY520, HY510, and HM510, respectively. These observations have been interpreted in terms of solid-state migration of cations present in clay interlayer space to zeolite extraframework sites during pelletization. Reexchange of cations in zeolites HY and HM with an aqueous solution of Na + /Ca 2+ salts shows sorption isotherms closer to the respective pelletized samples. X-ray diffraction studies of zeolites in powders as well as pellets confirm migration of clay cations to zeolite extraframework sites.

An Overview on Zeolite Shaping Technology and Solutions to Overcome Diffusion Limitations

“…Likewise, Jasra et al [30] studied the effect of a clay binder, as bentonite and attapulgite on the sorption and catalytic properties of zeolite X, Y, and MOR pellets. An increase in the heat of adsorption values upon pelletization was highlighted, which may be explained by the migration of clay cations within the zeolite cavities, thus decreasing the surface activity.…”

The curious case of zeolite–clay/binder interactions and their consequences for catalyst preparation

“…bentonite, kaolin and attapulgite) as a binder with zeolites, high-temperatures are used in the pelletization process in order to eliminate the activity of the clay and destroy the surface area, whilst creating meso-and/or macro-porosity. 26 However, it has been reported that a substantial decrease in the inter-and intra-crystalline acidity of the H-zeolite occurs during pelletization due to the neutralization of acid sites with mobile alkaline or alkaline-earth cations from the clay binder. 27 Clay has also been shown to decrease weak acidity and increase high strength acid site density, 28 as well as inuence product selectivity 29 and improve coke stability (by trapping coke precursors in the kaolinite binder).…”

Enhancement of Cerium exchange with Ultrasound

“…Figure 7 shows the X-ray diffractogram of the zeolites. The cation exchange resulted in the missing of some peaks due to the cerium oxide occluded on the crystal surface as mentioned in the literature [11,12]. This means that X-ray diffraction studies of the zeolites in powders confirm the migration of cerium to the extra-framework sites of Zeolite X.…”