Cu/ZrO2 catalysts obtained by impregnation of ZrO2 and complexation with citric acid were studied for CO2 hydrogenation to methanol. The catalyst structure, texture, and active copper surface were determined using XRD, BET, and reactive adsorption of N2O, respectively. The XPS and Auger spectroscopies were used to determine the surface structure and copper electronic state. FT-IR pyridine adsorption was studied to determine acidity of the catalysts. The results of quantum-chemical calculations concerning the formation of oxygen vacancies in monoclinic and tetragonal ZrO2 have been also presented. It was found that selection of the appropriate conditions of the catalyst preparation influences the degree of copper dispersion, its electronic state, and contents of the zirconia polymorphic phases (tetragonal and monoclinic). The presence of oxygen vacancies stabilizes both the thermodynamically unstable t-ZrO2 phase and Cu1+ cations, which are present in the vicinity of oxygen vacancies. Complexes formed preferentially on tetragonal ZrO2 built from Cu cations and oxygen vacancies are the acid centers active in methanol synthesis reaction; therefore the catalytic activity toward methanol increases with increasing t-ZrO2 content. The implications of the obtained results for the mechanism of the catalytic hydrogenation of CO2 are discussed.

The zeolite Beta is considered as a promising additive for FCC catalyst in diesel oil production. In this article, it is shown that hierarchical zeolite Beta obtained by an optimized desilication procedure increases Diesel and propylene yields during gas-oil cracking reaction.The alkaline treatment of zeolite Beta (Si/Al = 22) by desilication with NaOH and NaOH&TBAOH was investigated. The catalytic performance improvement of desilicated zeolite Beta has been rationalized by deep characterization of the samples including X-ray diffraction, low temperature adsorption of nitrogen, solid-state 29 Si MAS NMR and IR studies of acidity. Finally, the catalytic performance of the zeolites Beta was evaluated in the cracking of n-decane, 1,3,5-tri-iso-propylbenzene and vacuum gas oil. It was found that desilication with NaOH&TBAOH ensures the more uniform intracrystalline mesoporosity with the formation of narrower mesopores, while preserving full crystallinity resulting in catalysts with the most appropriated acidity and then, with better catalytic performance.

This work was aimed to evidence that substituted pyridine, 2,6-ditert-butylpyridine, is a suitable probe for the quantitative investigation of the external acidity in hierarchically structured zeolites. The 2,6-di-tert-butylpyridine was too large to enter the micropores, even in wide pore zeolites, and nearly no sites in nonmesoporous zeolites were available. Accessibility studies of acid sites in zeolites TNU-9 and BEA involving quantitative IR measurements with hindered 2,6-di-tertbutylpyridine as a probe were performed. The extinction coefficients of the 1615 cm −1 diagnostic bands of 2,6-di-tert-butylpyridine interacting with Brønsted acid sites were determined. Lewis acid sites were not detected with the probe. The accessibility factor (AF) for the 2,6-di-tert-butylpyridine probe molecule was defined as the number of sites detected by adsorption of the dTBPy (external sites) divided by the total amount of acid sites in the studied zeolites as quantified by pyridine sorption. Upon desilication resulting in the fabrication of the secondary mesopores, the enhanced accessibility of the protonic sites was observed. In comparison to the mesoporous zeolites with the secondary system of mesopores generated by alkaline leaching, considerably higher accessibility of protonic sites was evidenced in both ultrathin ZSM-5 and delaminated ITQ-2 zeolite.

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Elsevier Sadowska, K.; Góra-Marek, K.; Drozdek, M.; Kustrowski, P.; Datka, J.; Martínez-Triguero, J.; Rey Garcia, F. (2013). Desilication of highly siliceous zeolite ZSM-5 with NaOH and NaOH/tetrabutylamine hydroxide. ABSTRACTThe results of both chemical and XPS analysis pointed out that desilication of highly siliceous ZSM-5 of Si/Al = 164 was more effective in the surface zone than in the bulk, contrary to zeolite ZSM-5 of Si/Al = 31.6. According to the IR studies in parent zeolite the concentration of protonic sites was very close to the concentration of Al indicating that all Al atoms can form Si-OH-Al. The results of our quantitative IR studies strongly support the realumination thesis, i.e. some Al atoms extracted in basic solutions are subsequently reinserted forming new acidic hydroxyls. In desilicated zeolites all Al atoms were able to form protonic sites, however part of them dehydroxylated during the activation of zeolite producing Lewis acid sites according to the stoichiometry: one protonic site was transformed into one Lewis site. Low temperature nitrogen adsorption revealed that the treatment of highly siliceous zeolite with 0.2 M NaOH/TBAOH mixture produced mesopores of smaller diameter and narrower pore size distribution than in the case of zeolite of medium Si/Al ratio. This result can be explained by low concentration of Al which similarly as TBA + cations plays the role of pore directing agents (PDA). Contrary to TBA + , the presence of Al in desilication mixture, led to the formation of larger pores. Therefore, in highly siliceous zeolite TBA + played dominant role as PDA producing narrower pores. Highly siliceous zeolite with uniform distribution of relatively narrow pores may be useful catalyst or catalyst support. The influence of desilication temperature on porosity development was also investigated. The increase of desilication temperature from 338 K to 353 K resulted in both more extensive demetalation (more Si and Al is extracted) and the distinct increase of the volume and surface of mesopores. Both lower concentration of protonic sites and higher concentration of Lewis 2 sites confirmed partial zeolite destruction upon desilication at elevated temperature. The experiments of pivalonitrile sorption followed by IR spectroscopy showed a significant increase of accessibility of acid sites to bulky pivalonitrile molecules.