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1. Selective propylene oxidation to acrolein by gold dispersed on MgCuCr2O4 spinel

Author

Song, W., Perez Ferrandez, D.M., Haandel, van, L., Liu, P., Nijhuis, T.A., Hensen, E.J.M., Song, W., Perez Ferrandez, D.M., Haandel, van, L., Liu, P., Nijhuis, T.A., and Hensen, E.J.M.

Abstract

Gold nanoparticles supported on a MgCuCr2O4 spinel catalyze the aerobic oxidation of propylene to acrolein. At 200 °C, the selectivity is 83% at a propylene conversion of 1.6%. At temperatures above 220 °C, propylene combustion dominates. The good performance of Au/MgCuCr2O4 in selective propylene oxidation is due to the synergy between metallic Au and surface Cu+ sites. Kinetic experiments (H2 addition, N2O replacing O2) show that the reaction involves molecular oxygen. DFT calculations help to identify the reaction mechanism that leads to acrolein. Propylene adsorbs on a single Au atom. The adsorption of propylene via its p-bond on gold is very strong and can lead to the dissociation of the involved Au atom from the initial Au cluster. This is, however, not essential to the reaction mechanism. The oxidation of propylene to acrolein involves the oxidation of an allylic C–H bond in adsorbed propylene by adsorbed O2. It results in OOH formation. The resulting CH2–CH–CH2 intermediate coordinates to the Au atom and a support O atom. A second C–H oxidation step by a surface O atom yields adsorbed acrolein and an OH group. The hydrogen atom of the OH group recombines with OOH to form water and a lattice O atom. The desorption of acrolein is the most difficult step in the reaction mechanism. It results in a surface oxygen vacancy in which O2 can adsorb. The role of Cu in the support surface is to lower the desorption energy of acrolein.

Published
2015

2. Determination of the first apparent dissociation constant in waters with high ionic strength at 25.0ºC

Author

SANTOS, Paulo Guimarães Pereira dos., CAVALCANTI, Bernadete., and HAANDEL, Van.

Subjects
Tratamento de água, Processos químicos, Engenharia sanitária, Força iônica, Chemical processes, Water treatment, Ionic force
Abstract

Submitted by Deyse Queiroz (deysequeirozz@hotmail.com) on 2019-02-28T17:28:43Z No. of bitstreams: 1 PAULO GUIMARÃES PEREIRA DOS SANTOS - DISSERTAÇÃO PPGECA 1983..pdf: 4382872 bytes, checksum: 5dab63047b5789602c356377bd616f4c (MD5) Made available in DSpace on 2019-02-28T17:28:43Z (GMT). No. of bitstreams: 1 PAULO GUIMARÃES PEREIRA DOS SANTOS - DISSERTAÇÃO PPGECA 1983..pdf: 4382872 bytes, checksum: 5dab63047b5789602c356377bd616f4c (MD5) Previous issue date: 1983 A determinação da constante de dissociação de sistemas de ácidos ou bases ou sais realizada através de métodos manométricos e termodinâmicos somente pode ser aplicada para baixa forca iônica e à diluição infinita. Nesta tese, propõe-se determinar à 25°C a primeira constante aparente de dissociação de sistemas terciários de alta força iônica tais que: (A) NaCl + NaHCO3+H2O; {B}KCI + NaHC03+H20; (c) CaCl2 + NaHC03+H20 e (D)MgCl2 + NaHCO3 + H2O ; ou seja, águas naturais de alta salinidade. Como método experimental, utilizou-se a titulação de Gran na faixa de pH em que as duas funções matemáticas de interesse (F1 e F2) se aplicam; ou seja, 3.00 ph 6.35. Estas funções matemáticas permitiram a obtenção dos seguintes parâmetros: (i) coeficiente da atividade operacional de H+, fh+; (ii) volume de ácido forte (HCL) requerido até o ponto de equivalência de H2CO3, V1(ml) e (iii) primeira constante aparente de dissociação do sistema carbônico com espécies livres e complexa, K, respectivamente. O pH foi obtido com o uso de célula constituída por eletrodo de vidro acoplado à eletrodo de referência tipo calomelano saturado; ou seja, célula com junção líquida. A calibração do sistema de eletrodos foi feita, antes de cada experimento com as soluções teste, em uma solução padrão de baixa força iônica. Devido à diferença entre as matrizes iônicas das soluções padrão e teste, o pH foi interpretado em termos do Residual de Potencial de Junção Líquida ( RPJL). A influencia deste fator foi também incorporada ao modelo matemático das funções F1 e F2. Neste trabalho foi também proposta uma modelação para sistemas terciário de alta salinidade onde se aplicou a teoria de Loewenthal & Marais(10) para o sistema carbônico à baixa força iônica e com certas modificações. Estas se reportam a incorporação dos efeitos de força iônica, do RPJL e da formação de pares iônicos nas equações que definem estes sistemas. Os resultados obtidos, para fH+ apresentaram valores crescentes com o aumento de força iônica na faixa 0.1-« t * 3 . 0. Uma relação semeIhante foi obtida por Cavalcanto, 8 v H (4) para sistemas binários de cloretos 5 25°C e na mesma faixa de força iônica desta pesquisa. Os resultados experimentais finais obtidos mostraram que a constante K 1a aumenta com o aumento de força iônica. The determination of the dissociation constant of acid or base systems or salts performed by manometric and thermodynamic methods can only be applied for low ionic strength and infinite dilution. In this thesis, it is proposed to determine at 25 ° C the first apparent dissociation constant of high ionic strength tertiary systems such that: (A) NaCl + NaHCO 3 + H 2 O; KCl + NaHC03 + H20; (c) CaCl2 + NaHC03 + H2O and (D) MgCl2 + NaHCO3 + H2O; that is, natural waters of high salinity. As an experimental method, Gran titration was used in the pH range in which the two mathematical functions of interest (F1 and F2) apply; that is, 3.00 ph 6.35. These mathematical functions allowed to obtain the following parameters: (i) coefficient of the operational activity of H +, fh +; (ii) the volume of strong acid (HCL) required to the equivalence point of H2CO3, V1 (ml) and (iii) the first apparent decomposition constant of the carbonic system with free and complex species, K, respectively. The pH was obtained with the use of a cell composed of a glass electrode coupled to the reference electrode type saturated calomel; that is, cell with liquid junction. The calibration of the electrode system was done, before each experiment with the test solutions, in a standard solution of low ionic strength. Due to the difference between the ionic matrices of standard solutions and test, the pH was interpreted in terms of the Liquid Junction Potential Residual (RPJL). The influence of this factor was also incorporated into the mathematical model of the F1 and F2 functions. In this work it was also proposed a modeling for high salinity tertiary systems where the Loewenthal & Marais theory (10) was applied to the carbonic system at low ionic strength and with certain modifications. These report the incorporation of ionic force, RPJL and ion pair effects in the equations that define these systems. The results obtained for fH + showed increasing values ​​with the increase of ionic strength in the range 0.1 - t * 3. 0. A similar relationship was obtained by Cavalcanto, 8 v H (4) for binary systems of chlorides 5 25 ° C and in the same ionic strength range of this research. The final experimental results obtained showed that the constant K 1a increases with the increase of ionic strength.

Published
1983

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