Design of Novel Sulfated Nanozirconia Catalyst for Biofuel Synthesis

Abstract

We report on the elaboration of nanoparticulate SO 4 2– –ZrO 2 solid acid catalyst for conversion of free fatty acids into biofuel. Three different morphological modifications of zirconia were prepared with the sol–gel method and compared as acid supports: polydispersed nanopowder (PNP), monodispersed nanopowder (MNP), and monodispersed nanoparticles coating (MNC). The size-selected zirconia–oxo–alkoxy (ZOA) nanoparticles of 3.6 nm diameter were prepared in a rapid micromixing reactor and either precipitated (MNP) or deposited on glass beads (MNC). The polydispersed 4/100/500 nm ZOA particles were prepared in nonparent alcohol for realization of PNP powders. The grafting of SO 4 2– groups was realized on the three ZOA supports by wet impregnation method, and three catalysts were prepared after the subsequent drying and thermal treatment stages. The temperature of thermal treatment strongly affects the stability of the solid acid complex and serves to be an important factor of the preparation process. A strong retention of carbon on the surface of smallest zirconia nanoparticles induces their sintering, thus reducing the active area; therefore, the supported size-selected nanoparticles appear to be the best solution for realization of an efficient catalyst. The best acid complex stability in terms of reuse number was obtained with the thermal treatment temperature of ∼580 °C, and the specific activity (normalized on catalyst mass) of MNC catalyst toward palmitic acid conversion to methyl palmitate was found to be almost 2 orders of magnitude higher than that of PNP and MNP catalysts.