Catalytic Behavior of Rare-Earth Sulfates: Applications in Organic Hydrogenation and Oxidation Reactions

Abstract

Two isostructural ammonium rare-earth R double sulfate monohydrates NH4R(SO4)2·H2O, R = Y, Ho, have been hydrothermally synthesized at 170 °C for 1 week. The crystal structures established by single-crystal X-ray diffraction are monoclinic, space group P21/n, Z = 4, with unit cell parameters a = 10.2171(7) and 10.219(2) Å, b = 8.3349(5) and 8.338(1) Å, and c = 10.3267(7) and 10.323(2) Å, and β = 119.5290(10) and 119.482(3)°, for R = Y and Ho, respectively. The most interesting feature of the 3D structure is the existence of helical channels along the a direction, where isolated RO8 polyhedra alternate with the two kinds of sulfate groups, and the ammonium cations are located inside the channels. Their infrared and thermal stability analyses have also been performed. These materials behave as active catalysts in hydrogenation reactions of olefins and nitroaromatics, and in highly chemoselective, hydrogen peroxide mediated, oxidation of organic sulfides. High yielding, mild conditions of reactions, suitability for solid-phase reactions, and reusability with no detriment of selectivity, activity, or yield are among the advantages of these described solid catalysts.