La-Modified SBA-15 Prepared by Direct Synthesis: Importance of Determining Actual Composition

Abstract

La integration (at various nominal contents) in SBA-15 prepared under acidic medium was intended from corresponding direct nitrate addition during mesoporous silica formation. Materials were impregnated with Pt (1.5 w%) and studied through several textural (N2 physisorption), structural (XRD, TG-DTG) and surface (FTIR, STEM-HAADF, SEM-EDS, NH3 and CO2 TPD) instrumental techniques. Pt-impregnated solids were tested in phenol hydrodeoxygenation (HDO, T=250 °C, 3.2 MPa, batch reactor, n-decane as solvent). Catalytic activity (in pseudo first order kinetic constant, kHDO basis) was related to Pt dispersion which was, however, not determined by nominal rare earth content. Determining actual composition of modified SBA-15 materials is crucial in reaching sound conclusions regarding their physicochemical properties, especially when La modifier is directly added during mesoporous matrices formation where efficient interaction among constituents could be difficult to get. Otherwise, results from some characterization techniques (N2 physisorption and FTIR, for instance) could be misleading and even contradictory. Indeed, extant modifier precursors when under SBA-15 synthesis conditions could affect the properties of prepared materials even though they were absent in obtained| formulations. Performing a simple compositional analysis could eliminate uncertainties regarding the role of various modifiers on characteristics of final catalysts. However, several groups have failed in doing so.