Copper site energy distribution of de-NOx catalysts based on titanosilicate (ETS-10)

This study deals with copper-based catalysts prepared on a crystalline titanosilicate (ETS-10) matrix. Two samples prepared by ionic exchange, obtained by depositing different amounts of copper (6 and 11 wt%, corresponding to partial and total exchange, respectively), were selected for this study. Nitrogen monoxide was chosen as adsorbate to probe the surface properties of copper sites in terms of NO-Cu interaction energy. Microcalorimetric analysis of NO adsorption gave a direct measure of the NO-Cu energy of interaction and a view of the energy distribution of the copper sites from the differential and integral adsorption heat curves as a function of NO coverage. Initial heats of adsorption were around 110-130 kJ·mol-1 and fell down to 30-40 kJ·mol-1 at higher NO coverage. Volumetric isotherms of NO adsorption were measured at different temperatures (19-70 °C). A thermodynamic model was applied to the isotherms, making it possible to describe the NO-Cu site interaction energy by means of a function giving the number of Cu sites vs adsorption enthalpy, ΔaH. The high-loading copper sample had more energetic interaction with NO (-171 < ΔaH/kJ·mol-1 < -44), with a broader distribution, than the low-loading sample (-111 < ΔaH/kJ·mol-1 < -41). Parameters of adsorption, such as adsorption constant, molar entropy of adsorption, and half-coverage temperature at unit pressure (T°1/2), were obtained for each type of Cu site. The properties of the Cu sites were related with the activity measured in the reaction of selective catalytic reduction (SCR) of NO with ethylene.