Strain in Silica-Supported Ga(III) Sites : Neither Too Much nor Too Little for Propane Dehydrogenation Catalytic Activity

Altres ajuts: Acord transformatiu CRUE-CSICWell-defined Ga(III) sites on SiO are highly active, selective, and stable catalysts in the propane dehydrogenation (PDH) reaction. In this contribution, we evaluate the catalytic activity toward PDH of tricoordinated and tetracoordinated Ga(III) sites on SiO by means of first-principles calculations using realistic amorphous periodic SiO models. We evaluated the three reaction steps in PDH, namely, the C-H activation of propane to form propyl, the β-hydride (β-H) transfer to form propene and a gallium hydride, and the H-H coupling to release H, regenerating the initial Ga-O bond and closing the catalytic cycle. Our work shows how Brønsted-Evans-Polanyi relationships are followed to a certain extent for these three reaction steps on Ga(III) sites on SiO and highlights the role of the strain of the reactive Ga-O pairs on such sites of realistic amorphous SiO models. It also shows how transition-state scaling holds very well for the β-H transfer step. While highly strained sites are very reactive sites for the initial C-H activation, they are more difficult to regenerate. The corresponding less strained sites are not reactive enough, pointing to the need for the right balance in strain to be an effective site for PDH. Overall, our work provides an understanding of the intrinsic activity of acidic Ga single sites toward the PDH reaction and paves the way toward the design and prediction of better single-site catalysts on SiO for the PDH reaction. We performed computational calculations of Ga(III) single sites on realistic amorphous models of SiO to evaluate their catalytic activity toward the propane dehydrogenation reaction. Our results show that a balance in strain is key, in which neither too stiff nor too loose Ga−O bonding is needed to obtain the highest catalytic activity

Classification of 5-HT1A Receptor Ligands on the Basis of Their Binding Affinities by Using PSO-Adaboost-SVM

In the present work, the support vector machine (SVM) and Adaboost-SVM have been used to develop a classification model as a potential screening mechanism for a novel series of 5-HT1A selective ligands. Each compound is represented by calculated structural descriptors that encode topological features. The particle swarm optimization (PSO) and the stepwise multiple linear regression (Stepwise-MLR) methods have been used to search descriptor space and select the descriptors which are responsible for the inhibitory activity of these compounds. The model containing seven descriptors found by Adaboost-SVM, has showed better predictive capability than the other models. The total accuracy in prediction for the training and test set is 100.0% and 95.0% for PSO-Adaboost-SVM, 99.1% and 92.5% for PSO-SVM, 99.1% and 82.5% for Stepwise-MLR-Adaboost-SVM, 99.1% and 77.5% for Stepwise-MLR-SVM, respectively. The results indicate that Adaboost-SVM can be used as a useful modeling tool for QSAR studies

Strain in Silica-Supported Ga (III) Sites: Neither Too Much nor Too Little for Propane Dehydrogenation Catalytic Activity

Well-defined Ga(III) sites on SiO2 are highly active, selective, and stable catalysts in the propane dehydrogenation reaction. In this contribution, we evaluate the catalytic activity towards propane dehydrogenation of tri-coordinated and tetra-coordinated Ga(III) sites on SiO2 by means of first principles calculations using realistic amorphous periodic SiO2models. We evaluated the three reaction steps in propane dehydrogenation, namely the C-H activation of propane to form propyl, the beta-hydride elimination transfer to form propene, and a Ga-hydride, and the H-H coupling to release H2, regenerating the initial Ga-O bond and closing the catalytic cycle. Our work shows how Brønsted-Evans-Polanyi relationships are followed for these three reaction steps on Ga(III) sites on SiO2 and highlights the role of the strain of the reactive Ga-O pairs on such sites of realistic amorphous SiO2 models. While highly strained sites are very reactive sites for the initial C-H activation, they are more difficult to regenerate. The corresponding less strained sites are not reactive enough, pointing to the need of a right balance in strain to be an effective site for propane dehydrogenation. Overall, our work provides an understanding of the intrinsic activity of acidic Ga single sites towards the propane dehydrogenation reaction and paves the road towards the design and prediction of better single-site catalysts on SiO2 for the propane dehydrogenation reaction.</p