Ethanol dehydration over Keggin type tungstophosphoric acid and its potassium salts supported on carbon

Abstract

The current study reports the synthesis, characterization and catalytic activity of tungstophosphoric acid (HPW) and its potassium salts (KH2PW and K3PW) supported on activated carbon (AC). Because potassium salts of tungstophosphoric acid are insoluble, the carbon supported KH2PW and K3PW were prepared by a two step impregnation method. The synthesized catalysts were characterized by various physicochemical methods such as Fourier transform infrared and Raman spectroscopy, differential thermal analysis, thermogravimetric analysis, X-ray diffraction, scanning electron microscopy and nitrogen physisorption. It is observed that all active phases keep their Keggin-type structure after being supported on AC, while their specific surface area is considerably increased by deposition on this porous substrate. The results also indicated that the synthesized materials retained the morphology specific for the support as well as its thermal properties. The adsorption behaviour of the nanocomposites towards nicosulfuron pesticide was found to be particulary good and even slightly improved when compared to pure activated carbon. The catalytic activity of the prepared catalysts was probed for the vapor phase dehydration of ethanol at 300 °C. The conversion of ethanol and selectivity toward ethylene and diethyl ether of nanocomposites were compared with the values of bare HPW, KH2PW and K3PW. Results revealed that catalytic activity depends on the catalyst type and active phase loading. The conversion over unsupported catalysts decreased by increasing the cation content per Keggin unit. The nanocomposites with 30 wt% loading of HPW achieved the best conversion of nearly 100% and the highest and stable selectivity toward ethylene. The catalytic activity of nanocomposites with acidic KH2PW showed lower catalytic activity of about 70%, while the nanocomposites of neutral K3PW and AC showed negligible activity.