Ionic liquid-assisted immobilization of Rh on attapulgite and its application in cyclohexene hydrogenation

Rhodium-attapulgite (Rh-Atta) catalyst was prepared by immobilizing Rh3+ on Atta via an ionic liquid (IL), 1,1,3,3-tetramethylguanidine lactate (TMG(+)L(-)), followed by reduction with hydrogen at 300 degrees C. The resulting composite was characterized by different techniques. X-ray photoelectron spectroscopy analysis showed that the loaded rhodium on Atta existed mainly in the form of Rh-0 with a small amount of its oxides and was distributed uniformly on Atta with a particle size of less than 5 nm, as confirmed by transmission electron microscopy examination. X-ray diffraction analysis indicated that the layered channel structure of Atta was destroyed to some extent due to the impregnation of the IL and Rh. IR spectra indicated that the Lewis and Bronsted acid sites in Atta absorbed the TMG(+) ions chemically. The specific surface areas determined by the BET method from N-2 sorption isotherms decreased with the entrance of the IL and loaded Rh. The activity of the composite for cyclohexene hydrogenation was investigated, which exhibited much higher efficiency compared to those of other catalysts, and the turnover frequencies reached 2700 (mol of cyclohexene/mol of Rh)/h.