Preparation and characterization of chromium-doped magnesium fluoride catalysts via an aqueous sol–gel method

High surface area Cr 3+ -doped MgF 2 catalysts were synthesized from an aqueous sol–gel method under mild conditions. The amount of Cr 3+ doped in the investigated CrF 3 /MgF 2 catalysts covered a wide range of mole concentration ranging from 0 to 25 mol% to reveal its effect on the properties of the catalysts. The physio-chemical properties of the CrF 3 /MgF 2 catalyst were examined by means of N 2 gas sorption, X-ray powder diffraction (XRD), energy dispersive spectrometer (EDS), and temperature-programmed desorption (TPD) of NH 3 . XRD analysis indicates that the doping of Cr 3+ resulted in reduced crystallinity but did not change the original crystalline structure of MgF 2 . Doping of Cr 3+ (8–25 mol%), on the other hand, can increase the surface area of CrF 3 /MgF 2 significantly to ~300 m 2 /g from ~50 m 2 /g of the nondoped MgF 2 . There is also significant amount of Lewis acid sites formed upon incorporation of Cr 3+ into MgF 2 lattice, which was evidenced from the NH 3 -TPD results. The catalytic activity of the 25 mol% Cr 3+ -doped MgF 2 catalyst on the dehydrofluorination reaction of 1,1-difluoroethane (HFC-152a, CH 3 CHF 2 ) has reached a conversion rate of ~57%, which is over two times higher than the undoped MgF 2 catalyst. Furthermore, the 25 mol% Cr 3+ -doped MgF 2 catalyst has been successfully tested over 210 h upon the dehydrofluorination of CH 3 CHF 2 at 300 °C with the conversion rate remain greater than ~45%.