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Three different ordered mesoporous silica materials, such as MCM-41, Al containing MCM-41 (mass ratio Si/Al = 10) and SBA-15, were prepared. In a next step, cobalt (5-8 wt%) as an active metal for redox reactions, was introduced by the impregnation. The prepared catalysts were characterized by AAS, EDX, N-2 physisorption, XRD, DR UV-Vis spectroscopy, Raman spectroscopy, TPR-H-2 and their catalytic properties were evaluated for N2O decomposition and reduction. The catalysts showed poor activity in N2O decomposition while the use of reducing agent (carbon monoxide) was beneficial for their catalytic activities. The lowest catalytic activity showed Co/Al-MCM indicating that the aggregated CoxOy species present in this catalyst were inactive and not beneficial for the catalytic activity.

Introduction - Zeolites and mesoporous materials are widely used as catalysts or separating agents in the refining and petrochemical industries. The understanding of adsorption phenomena is critical in the comprehension and the modeling of reaction kinetics. Selectivity and adsorption efficiency are often characterized by Henry constants and adsorption enthalpies. It would therefore be advantageous if one could, for a preliminary evaluation, estimate the adsorption properties of mesoporous materials for various hydrocarbons. In this work, partial least square regression has been performed using structural and topological descriptor sets [1] to obtain predictive models for the adsorption properties of mesoporous materials and adsorbate molecules in gas phase. Experimental - Adsorption enthalpies and Henry constants used for modeling were experimentally obtained for MCM-41, MCM-48, PHTS, SBA-15 for a set of linear and branched alkanes (20-23 molecules). The training set (10 molecules) was selected bya clustering analysis to contain as much variance as possible from the descriptor set. A structural (number of carbon atoms, Kappa and Chi indices) or topological (number of carbon atoms and branching factors) descriptor set was used. The models were validated by "Leave-One-Out" cross-validation and external validation with the prediction set. Logarithmic values were used for the Henry adsorption constants during the modeling process. Results and discussion - Generally, models based on both descriptor sets yielded similar results for adsorption enthalpies but use of topological descriptor sets offers a more straightforward interpretation of the model's coefficients. A clear influence of branching factors in the model's coefficients was observed. Predicting accuracies approaching the experimental error or better were obtained for these non-shape selective materials. The modeling of Henry constants reveals a significantly higher accuracy for the structural descriptor set. Addition of a physicochemical descriptor set (e.g. vapor pressure) enhances the predictability of the models. Conclusion - Models established by partial least square regression and few descriptors describe the gas phase adsorption of linear and branched alkanes on mesoporous materials both qualitatively and quantitatively. The use of a topological set of descriptors gives new insights in the influence of branching factor towards selectivity. The presented models are useful with respect to the prediction of adsorption properties for separation or catalytic processes. Acknowledgements - Joeri Denayer is grateful to FWO Vlaanderen, Tim Duerinck wishes to thank IFP for its financial and scientific support. [1] P.Leflaive et al, Microporous and Mesoporous Materials 132 (2010) 246. E-mail corresponding author: Tim.Duerinck@vub.ac.be

In this study we report the synthesis of a series of composite nanostructures comprising LDH and TiO2 phases. The materials characterization showed that the LDH crystallites are encapsulated inside the TiO2 matrix after the anatase seeds are deposited on Mgx Al-LDHs. The structure in which LDH phase is embedded into anatase matrix is unique bringing important advantages to the photocatalytic performances of the nanocomposites. The photocatalytic activity of the prepared nanocomposites was tested on the degradation of the methylene blue (MB) in aqueous solution. The photocatalytic activities of the nanocomposites were compared with commercial TiO2 nanoparticles Degussa P25. The nanocomposites exhibited superior photocatalytic activity in basic environment because the negatively charged surface of TiO2 nanoparticles at high pH attracts the positively charged methylene blue species.

We present an efficient method for the quantification of crystalline versus amorphous phase content in mesoporous materials, making use of electron energy loss spectroscopy. The method is based on fitting a superposition of core-loss edges using the maximum likelihood method with measured reference spectra. We apply the method to mesoporous TiO2 samples. We show that the absolute amount of the crystalline phase can be determined with an accuracy below 5%. This method takes also the amorphous phase into account, where standard X-ray diffraction is only quantitative for crystalline phases and not for amorphous phase. (c) 2006 Elsevier B.V.. All rights reserved.