The Temperature Programmed Desorption (TPD) was used to determine the acidity and the acid strength of zeolites (H-ZSM-5, H-Ferrierite, HM-20 and HY-5.6(2)), supported metal zeolites (1% Cu/H-ZSM-5, 1% Pd/H-ZSM-5, 1% Pt/H-ZSM-5, 1% Cu/H-Ferrierite, 1% Pd/H-Ferrierite, 1% Pt/H-Ferrierite), and catalyst supports (TiO2 และ Al2O3). Ammonia gas was adsorbed at room temperature and desorbed at 600 C at constant heating rate of 12C/min. From the TDP results, the acidities of zeolites vary with SiO2/Al2O3 ratio. The lower SiO2/Al2O3 ratio causes the stronger acidity. The HY-zeolite with low SiO2/Al2O3 ratio of 5.6 exhibited high acidity of about 0.008 mol/gcat. It also showed a broad range of temperature of the ammonia desorption peak which might be attributed to the existing of wide ranges of acid strength. Due to the close ratio of SiO2/Al2O3, the H-ZSM-5, H-Ferrierite and HM-20 showed acidity of about 0.003-0.004 mol/gcat. The H-ZSM-5 and H-Ferrierite exhibited two kinds of acid sites: a weak acid site at the temperature ranges of 100-200C, and a strong acid site at 400-600C.
The HM 20 and the catalyst supports (TiO2 and Al2O3, non zeolite) possessed 1 ammonia desorption peak indicating they had 1 weak acid site. Their acid strengths were found in the temperature ranges of 100-200C. From this work the 1 wt% precious metals (Cu, Pd and Pt) impregnated on zeolites did not show the effect on the acidity and acid strength. This might be because of the insufficient loading.
By
Shuesri Jubjainai
