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Abstract: The influence of rare earth (RE) elements on the acidic properties of H-MCM-22 and H-Beta was studied by pyridine adsorption followed by infrared spectroscopy (FTIR) and n-heptane cracking, as a model reaction. The zeolites were submitted to ion exchange with rare earth nitrate solutions of La, Nd and Yb. The FTIR spectra of REH-MCM-22 indicate the presence of RE elements inside supercages and in the sinusoidal channels of the zeolite. After pyridine adsorption two additional bands are detected in REH-MCM-22 and REH-Beta, related to pyridine bonded to RE3+ cations. The n-heptane cracking reaction shows that the effect of rare earth elements is related not only to the acidity but also with the porous structure of both zeolites. In H-Beta zeolite, the presence of RE elements enhances the acidity of the catalysts. In H-MCM-22 zeolite, the most relevant effect of rare earth elements is on the shape selectivity that becomes more pronounced with the ionic radius of the RE elements. The nature of the coke deposited on the two materials shows distinct profiles that are also related to its porous structure. [Copyright &y& Elsevier]

Hierarchical SAPO-11 was synthesized using a commercial Merck carbon as template. Oxidant acid treatments were performed on the carbon matrix in order to investigate its influence on the properties of SAPO-11. Structural, textural and acidic properties of the different materials were evaluated by XRD, SEM, N 2 adsorption, pyridine adsorption followed by IR spectroscopy and thermal analyses. The catalytic behavior of the materials (with 0.5 wt.% Pt, introduced by mechanic mixture with Pt/Al 2 O 3 ), were studied in the hydroisomerization of n -decane. The hierarchical samples showed higher yields in monobranched isomers than typical microporous SAPO-11, as a direct consequence of the modification on both porosity and acidity, the later one being the most predominant. [ABSTRACT FROM AUTHOR]

Abstract: The activity and selectivity of bi-functional carbon-supported platinum catalysts for the hydroisomerization of n-alkanes have been studied. The influence of the properties of the carbon support on the performance of the catalysts were investigated by incorporating the metallic function on a series of carbons with varied porosity (microporous: GL-50 from Norit, and mesoporous: CMK-3) and surface chemistry (modified by wet oxidation). The characterization results achieved with H2 chemisorption and TEM showed differences in surface metal concentrations and metal–support interactions depending on the support composition. The highest metal dispersion was achieved after oxidation of the carbon matrix in concentrated nitric acid, suggesting that the presence of surface functional sites distributed in inner and outer surface favors a homogeneous metal distribution. On the other hand, the higher hydrogenating activity of the catalysts prepared with the mesoporous carbon pointed out that a fast molecular traffic inside the pores plays an important role in the catalysts performance. For n-decane hydroisomerization of long chain n-alkanes, higher activities were obtained for the catalysts with an optimized acidity and metal dispersion along with adequate porosity, pointing out the importance of the support properties in the performance of the catalysts. [Copyright &y& Elsevier]

Abstract: The effect of several desilication experimental parameters (base concentration, temperature and time) on the characteristics of MOR zeolite was studied. The samples were characterized by X-ray diffraction, 27Al and 29Si MAS-NMR, chemical analysis, and FTIR (framework vibration region). The textural characterization was made by N2 adsorption and the acidity was evaluated by pyridine adsorption followed by FTIR and by the catalytic model reaction of n-heptane cracking. The alkaline treatments promoted the Si extraction from the zeolite framework, without considerable loss of crystallinity and, as it was envisaged, an important increase of the mesoporous structure was attained. A linear correlation between the number of framework Si per unit cell, N Si, and the asymmetric stretching wavenumber, ν 1, was observed. The acidity characterization shows that the desilicated samples exhibit practically the same acid properties than the parent HMOR zeolite. The optimum desilication conditions were those used to obtain sample M/0.2/85/2, i.e., sample treated with 0.2M NaOH solution at 85°C for 2h. [Copyright &y& Elsevier]