Temperature-programmed desorption, SAPO

Catalysts Characterization. Following pretreatment of the SAPO molecular sieves, the catalysts were characterized by temperature programmed desorption (TPD) of ammonia and infrared spectroscopy. To assess the acidity of the samples, the desorption of ammonia from the catalysts was performed in a manner similar to that described by van Hooff et. al. [11]. For the ammonia TPD experiments, typically 0.1 gram of the molecular sieve sample was supported on quartz wool inside a 9 mm O.D. quartz reactor equipped with axial thermowell which contacted the top of the... 

Acidity of the SAPO-31 and Pt impregnated SAPO-31 was characterized by temperature programmed desorption (TPD) of ammonia by an earlier reported procedure. ... 

Moreover the decreases in intensity of the B peak with Si content (table 1) allowed us to suggest that the corresponding P atom (PI) is substituted for Si in the SAPO-11 framework. For Si content increasing acidity as determined by Temperature Programmed Desorption of Ammonia (TPDA) was observed to increase and then to decrease (37). It is quite probable that Si substitutes first P at PI atom position creating acidic site and then substitutes nearby At resulting in Si substituted as pairs and then in a decrease in acidity. Such a substitution on site PI was also proposed for Mn AIPO4-5 materials (39). 

We have examined temperatured-programmed desorption (TPD) and thermogravimetric analysis (TGA) of isopropyiamine on a series of Si-, Co-, and Mg-substituted AIPO-5 samples. The TPD-TGA results on the substituted samples show ammonia and propene desorbing in a well-defined feature between 575 and 650K, a feature not observed on pure AIPO-5. The results suggest that TPD-TGA measurements of isopropyiamine may be useful in determining the framework concentrations and acid site densities for SAPO-5, CoAPO-5, and MAPO-5. 

The catalytic activity of the protonic forms of SAPO-37 and HY zeolite were compared in the cracking of n-heptane and 2,2,4-trimethylpentane. HY zeolite presents a higher initial activity which is in agreement with its higher acidity characterized by temperature programmed desorption of ammonia. This is confirmed by the fact that SAPO-37 exhibits a higher relative cracking activity (2,2,4-trimethylpentane/n-heptane) than HY zeolite. 

Figure 2. Temperature Programmed Ammonia Desorption - plots of SAPO-5, ALPO-5-P and NH4 -ZSM-5. Nitrogen fiow rate 10 ml/min heating rate 5 C/min.

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