Study of basicity characterization on the surface of catalysts using probe molecule adsorption

Abstract

Basicity measurement of the catalyst surfaces by pyrrole adsorption has been studied. The difference of IR signals due to the adsorption of pyrrole, which was used as a probe molecule, on Brönsted basic sites and Lewis basic sites was investigated over MgO and Ca(OH)₂ as the representations of metal oxide and metal hydroxide catalysts, respectively. The analysis was performed in both qualitative, by FT-IR, and quantitative, by gas chromatograph analysis. The experimental results from FTIR measurement show that the effective time for pyrrole vapour introduction was approximately 10 minutes, and the suitable time for evacuation after pyrrole vapour introduction was found to be 90 minutes. In case of quantitative analysis, the amount of CO₂ adsorption was measured to compare to the adsorption of pyrrole using gas chromatograph. Results observed from the identical quantities of MgO, Na-Y and Ca (OH)₂ show that the amount of CO₂, in mole, adsorbed on the catalyst surfaces was more amount than pyrrole. On the contrary in case of Na-mordenite, the catalyst surface preferrably adsorbed pyrrole more than CO₂. The experimental results, showed that the distinction of IR spectra between Brönsted basic sites and Lewis basic sites could not obviously be analyzed by pyrrole adsorption technique.