Factors influencing the charge distribution on PdxPty bimetallic nanoparticles

AbstractWe performed quantum mechanics calculations to elucidate the electronic behavior of Pd-Pt bimetallic nanoparticles, using density functional theory, in response to particle size and stoichiometric composition. Using neutrally charged nanoparticles and the Bader charge analysis, we found that external Pd atoms were positively charged, which agrees with previous XPS observations of supported Pd-Pt nanoparticles. From the calculations, unsupported nanoparticles exhibit an electron transfer from Pd to Pt. This result supports the idea that Pd electron-deficient species are possibly responsible of the hydrogenating function of these catalysts, in the hydrodesulfurization of dibenzothiophene. Additionally, it was found that the particle size does not affect the electronic charge distribution and the stoichiometric composition is the factor that greatly influences this property in nanoparticles.Keywords: Pd-Pt nanoparticles, Bader charge analysis, DFT, bimetallic clusters.Factores que influyen en la distribución de carga en nanopartículas bimetálicas de PdxPtyResumenSe llevó a cabo la simulación del comportamiento electrónico de nanopartículas bimetálicas de Pd-Pt mediante cálculos mecanocuánticos, utilizando la teoría del funcional de densidad, con el fin de predecir la influencia en dicho comportamiento, de factores como el tamaño y la composición estequiométrica de la nanopartícula. Al considerar nanopartículas con carga neutra, se encontró, mediante el análisis de cargas de Bader que los átomos externos de Pd presentan una carga positiva, lo cual concuerda con análisis experimentales mediante XPS de catalizadores de Pd-Pt soportados. De las simulaciones, se encontró que las nanopartículas exhiben una transferencia de carga del Pd al Pt. Este resultado da crédito a la idea que especies electrodeficientes de Pd son las responsables de la función hidrogenante, de estos catalizadores, en la hidrodesulfuración del dibenzotiofeno. También se encontró que la influencia del tamaño de la nanopartícula no afecta la distribución electrónica, y que la composición estequiométrica es el factor que más influye en dicha propiedad de las nanopartículas.Palabras clave: nanopartículas Pd-Pt, análisis de cargas de Bader, DFT, clusters bimetálicos

Factors influencing the charge distribution on PdxPty bimetallic nanoparticles

AbstractWe performed quantum mechanics calculations to elucidate the electronic behavior of Pd-Pt bimetallic nanoparticles, using density functional theory, in response to particle size and stoichiometric composition. Using neutrally charged nanoparticles and the Bader charge analysis, we found that external Pd atoms were positively charged, which agrees with previous XPS observations of supported Pd-Pt nanoparticles. From the calculations, unsupported nanoparticles exhibit an electron transfer from Pd to Pt. This result supports the idea that Pd electron-deficient species are possibly responsible of the hydrogenating function of these catalysts, in the hydrodesulfurization of dibenzothiophene. Additionally, it was found that the particle size does not affect the electronic charge distribution and the stoichiometric composition is the factor that greatly influences this property in nanoparticles.Keywords: Pd-Pt nanoparticles, Bader charge analysis, DFT, bimetallic clusters.Factores que influyen en la distribución de carga en nanopartículas bimetálicas de PdxPtyResumenSe llevó a cabo la simulación del comportamiento electrónico de nanopartículas bimetálicas de Pd-Pt mediante cálculos mecanocuánticos, utilizando la teoría del funcional de densidad, con el fin de predecir la influencia en dicho comportamiento, de factores como el tamaño y la composición estequiométrica de la nanopartícula. Al considerar nanopartículas con carga neutra, se encontró, mediante el análisis de cargas de Bader que los átomos externos de Pd presentan una carga positiva, lo cual concuerda con análisis experimentales mediante XPS de catalizadores de Pd-Pt soportados. De las simulaciones, se encontró que las nanopartículas exhiben una transferencia de carga del Pd al Pt. Este resultado da crédito a la idea que especies electrodeficientes de Pd son las responsables de la función hidrogenante, de estos catalizadores, en la hidrodesulfuración del dibenzotiofeno. También se encontró que la influencia del tamaño de la nanopartícula no afecta la distribución electrónica, y que la composición estequiométrica es el factor que más influye en dicha propiedad de las nanopartículas.Palabras clave: nanopartículas Pd-Pt, análisis de cargas de Bader, DFT, clusters bimetálicos

Identification of Refractory Weakly Basic Nitrogen Compounds in a Deeply Hydrotreated Vacuum Gas Oil and Assessment of the Effect of Some Representative Species over the Performance of a Ni–MoS₂/Y-Zeolite–Alumina Catalyst in Phenanthrene Hydrocracking

Heavy crude oil processing leads the way in current refining. These crudes yield larger amounts of distillable heavy fractions such as vacuum gas oil (VGO). VGO must be treated in at least two refining units: a hydrotreating unit where sulfur, nitrogen, and other heteroatoms are removed, and a hydrocracking unit where suitable fuels are obtained. Removal of heteroatoms during hydrotreating, particularly, nitrogen, dictates the efficiency of hydrocracking. In the first part of this work, the nature of refractory nitrogen-containing compounds on the performance of a hydrotreating catalyst was evaluated. To achieve this goal, both a VGO and its hydrotreated counterpart were studied using electrospray ionization with Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR-MS). Weakly basic N-containing compounds, namely, heavy pyrrolic-like compounds and their partially hydrogenated derivatives, were found to be the most refractory to hydrotreating. These compounds are weakly basic compared to most nitrogen compounds present in VGO. Considering this finding, the second part of the work was devoted to assessing the effect of pyrroles on the reactivity of phenanthrene over a Ni–MoS₂/Y-zeolite–alumina two-stage hydrocracking catalyst. Tests were carried out in a fixed-bed reactor using mixtures of carbazole and tetrahydrocarbazole. Results showed that these compounds can affect the catalytic performance of Ni–MoS₂/Y-zeolite–alumina by reducing its activity and inhibiting its selectivity to hydrocracking products. These findings draw attention to the possible role of weakly basic nitrogen compounds in the catalytic performance of materials employed for two-stage hydrocracking units

In Situ IR-ATR Study of the Interaction of Nitrogen Heteroaromatic Compounds with HY Zeolites: Experimental and Theoretical Approaches

status: publishe

Handgrip strength and all-cause dementia incidence and mortality: findings from the UK Biobank prospective cohort study

Background: This study aimed to investigate the associations of grip strength with incidence and mortality from dementia and whether these associations differ by sociodemographic and lifestyle factors. Methods: A total of 466 788 participants of the UK Biobank (median age 56.5 years, 54.5% women). The outcome was all-cause dementia incidence and mortality and the exposure was grip strength. Grip strength was assessed using a Jamar J00105 hydraulic hand dynamometer. Results: Excluding the first 2 years of follow-up (landmark analysis), mean follow-up was 9.1 years (inter-quartile range: 8.3; 9.7) for incidence and 9.3 (inter-quartile range: 8.7; 10.0) for mortality. During this time, 4087 participants developed dementia, and 1309 died from it. Lower grip strength was associated with a higher risk of dementia incidence and mortality independent of major confounding factors (P < 0.001). Individuals in the lowest quintile of grip strength had 72% [95% confidence interval (CI): 1.55; 1.92] higher incident dementia risk and 87% [95% CI: 1.55; 2.26] higher risk of dementia mortality compared with those in the highest quintile. Our PAF analyses indicate that 30.1% of dementia cases and 32.3% of dementia deaths are attributable to having low grip strength. The association between grip strength and dementia outcomes did not differ by lifestyle or sociodemographic factors. Conclusions: Lower grip strength was associated with a higher risk of all-cause dementia incidence and mortality, independently of important confounding factors