Study Of Dehydroisomerization Of N-Butane And Corresponding Metal-Molecular Sieve Bifunctional Catalysis

The activation and utilization of alkanes is one of the important aspects in the field of catalyzing. The bifunctional catalysts with acid support and supported metal are needed in these reactions. In recent years, the transformation of n-butane has drawn a lot attraction. The isomerization and dehydroisomerization of n-butane have been studied and the latter reaction is thought to be more economical for the production of isobutene. The reactions such as activation, isomerization and deydroisomerization are involved in the direct transformation of n-butane, so the catalytic system with acidic function and metallic function has been employed for this direct transformaton. In the present work, based on the catalytic transformation of n-butane, the bifunctional catalysts have been widely tested and the interaction of the supported metal and the acid support in the bifunctional catalysts has been studied with the techniques such as NH3-TPD, IR, MAS NMR, XPS, XRD, physical adsorption, CO pulse chemical adsorption and TPR.In the catalytic tranformation of n-butane, Pd modified silicoaluminate molecular sieves were tested for n-butane's isomerization and dehydroismerization. The direct transformation of n-butane to isobutene can not been realized satisfactorily over these catalysts based on the zeolites, so several kinds of aluminophosphate molecular sieves and silicoaluminophaste molecular sieves were synthesized and employed as the acid support of the catalysts. With the catalytic property comparison of the Pd modified molecular sieves with different pore structure and acidity, the Pd/SAPO-lls, Pd/MeAPO-lls and Pd/MeAPSO-lls were confirmed to be the most suitable catalytic system. For Pd/SAPO-11, the effect of Si content of SAPO-11 on the framework element coordination, acidity, pore distribution and catalytic properties were tested. The acidity of SAPO-11 and catalytic properties of Pd/SAPO-11 changed with the Si content and extreme values of these properties can be obtained. The metal incorporation was also investigated. The element, Ti, Fe, Mg,Co and Mn were incorporated into the A1PO-11 and SAPO-11. The Pd/MnAPO-11 showed the highest selectivity for the dehydroisomerization products and Pd/MnAPSO-11 showed the highest catalytic activity and isomerization selectivity. It was found that the manganese incorporation not only changed the acidity of the molecular sieves, but also weakened the metallic properties of the supported Pd. Some interaction may exist between incorporated Mn and the supported Pd, According to the reaction results, the catalytic effect of supported Pd on the n-butane's activation is indispensable for the transformation.The characterization results and the catalytic performances of the bifunctional catalysts showed that the structure, surface properties and acidity of the molecular sieve had effect on the metallic proprieties of the supported metal and the catalytic properties. The interaction mechanism of the molecular sieves and the supported metal was brought forward to explain the catalytic action of the bifunctional catalysts in the n-butane's transformation. The proton difference of the hydroxyl group of the molecular sieves, the possible structure of the "metal-proton adduct" and related catalytic properties were also investigated and discussed. Different interaction between the support and the supported metal particles yields different cooperative catalysis and furthermore yields different transformations.