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Thermal behaviour of mixed Sn and Ge phosphates
Correlations with their catalytic properties
Abstract
Pure and mixed Ge and Sn hydrogenphosphates, prepared either by refluxing in 8M H3PO4 or by hydrothermal treatment at 180° or 300°C, have been characterized in terms of chemical composition and thermal behaviour and also tested as catalysts in the 1-butene isomerization, in order to correlate acidic properties with preparation method. Solid solutions for every composition in this system are formed only when using the refluxing method, as proved by X-ray and TG-DTA data. The hydrothermal treatments are strongly influenced by the hydrolysability of the Ge phosphate: in almost all the samples, where Ge was present, GeOHPO4 was identified on TG-DTA curves by the endothermic H2O weight loss at 700°–800°C. The acidic properties of the various materials decrease as GeOHPO4 content increases.
Abstract
The present work deals with preliminary studies concerning a new synthesis approach to prepare SAPO materials with AEL structure and evaluate their catalytic behavior in the hydroisomerization of long paraffins. The new SAPO-11 catalysts were synthesized with the help of a small amine (methylamine, MA) added during the preparation of the initial gel. As MA incorporates into the structure of the final materials, it contributes, together with DPA (dipropylamine), to an increase in Si incorporation as isolated species, which results in Brønsted acid sites. Thus, this new and original synthesis strategy allows to obtain materials with enhanced Brønsted acidity when compared with free MA materials. The catalysts were tested in n-decane hydroisomerization (n-decane was used as a model molecule) and confirmed the effect of MA on the acidic properties of the catalysts. The samples synthesized with MA present a higher number of acid sites that increase the catalytic conversion but have a negative effect in the isomerization selectivity, i.e. a more significant amount of cracking products is formed.
Losanka, P., Pancheval, T., Uzunova, A. (1997) Salicylic acid, properties, biosynthesis and physiological role. Bulg. J. Plant Physiol. 23 , 85-93. Salicylic acid, properties, biosynthesis and physiological role
-nanoparticles boundaries, leading to diminishing pore volume and surface area. The NH 3 -TPD results for acidic properties are shown in Table 2 and presented in Fig. 1 . There is one asymmetric broad peak in the range of 150–500 °C on TPD profiles of Al-HMS samples
addition of metal ion dopants such as Ga [ 5 ] and Ru [ 6 ], adding C 2 H 6 [ 7 ] or CO 2 as the co-feed of methane, [ 8 ], dealumination treatment for modifying the acidic properties of zeolite [ 9 ], silanation of external acid sites in H-ZSM5 [ 10
Effect of protonation and deprotonation on surface charge density of Nb2O5
A thermodynamic approach
niobium penaoxide . Bull Chem Soc Jpn . 1983 ; 56 : 2927 – 2931 . 10.1246/bcsj.56.2927 . 7. Datka , J , Turek , AM , Jehng , JM , Wachs , IE . Acidic properties of supported
. 14. Souza , MJB , Silva , AOA , VJ Fernandes Jr , Araújo , AS . Acid properties of AlMCM-41 molecular sieves with different sílica-alumina ratios by thermogravimetry . J Therm Anal Calorim . 2005 ; 79 : 425 – 428
, B , Szombathely , MV , Hoffmann , J , Brauer , P . 1995 Characterization of the acidic properties of zeolites by means of temperature-programmed desorption (TPD) of ammonia. Calculation of distribution function of the desorption energy . J
the surface, the groups with acidic properties also appear. Therefore, it can be assumed that in the deposited samples ZrP itself influences on the surface charge more than a support. Conclusions The
. It is known that catalytic activity of oxides can be related to the cooperative action of an oxidizing function and an acidic function. From this perspective, the determination of both redox and acidic properties of the catalytic centers becomes of
