ABSTRACT
Monometallic and bimetallic Cu:Ni catalysts with different Cu:Ni molar ratios (3:1, 2:1, 1:1, 1:2, 1:3) were synthesized by wetness impregnation on activated carbon and characterized by TPR (temperature programmed reduction), XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy). The synthesized catalysts were evaluated in the gas phase production of diethyl carbonate from ethanol and carbon dioxide. The largest catalytic activity was obtained over the bimetallic catalyst with a Cu:Ni molar ratio of 3:1. Its improved activity was attributed to the formation of a Cu-Ni alloy on the surface of the catalyst, evidenced by XPS and in agreement with a previous assignment based on Vegard law and TPR analysis. During the reaction rate experiments, it observed the presence of a maximum of the reaction rate as a function of temperature, a tendency also reported for other carbon dioxide-alcohol reactions. It showed that the reaction rate-temperature data can be adjusted with a reversible rate equation. The initial rate as a function of reactant partial pressure data was satisfactorily adjusted using the forward power law rate equation and it was found that the reaction rate is first order in CO2 and second order in ethanol.
ABSTRACT
Resumen Se sintetizó el catalizador Cu/MCM-41 mediante impregnación húmeda incipiente y se caracterizó por DRX, XPS, TPD-NH3 y adsorción-desorción de N2. Se evaluó el efecto de diferentes condiciones de reacción (temperatura, tiempo, tipo de solvente y cantidad de catalizador) en la isomerización del epóxido de α-pineno para la obtención de aldehído canfolénico con el catalizador Cu/MCM-41, que no había sido reportado previamente para este tipo de reacción. Se partió de un diseño experimental central compuesto mediante análisis de superficie de respuesta. Se encontró que la mejor selectividad fue de 85% (5 mg de catalizador; 70 °C; 0,5 h y el uso de acetato de etilo como solvente). Adicionalmente, se determinaron los principales factores y sus combinaciones que tenían mayor significancia en la síntesis del aldehído ajustado a un modelo polinomial de segundo grado. Se encontró que los factores que tienen mayor influencia en la conversión son la cantidad de catalizador, tiempo de reacción, el tipo de solvente y el factor combinado entre la cantidad de catalizador y el tipo de solvente. En el caso de la selectividad hacia el producto deseado no se encontró ningún factor significativo.
Abstract The Cu/MCM-41 catalyst was synthesized by incipient wet impregnation and characterized by XRD, XPS, TPD-NH3, and N2 adsorption-desorption. The effect of different reaction conditions (temperature, time, type of solvent, and amount of catalyst) on the isomerization reaction of α-pinene epoxide was evaluated to obtain camphoric aldehyde with the Cu/MCM-41 catalyst, which had not been previously reported for this kind of reaction. The experiment was based on a central composite experimental design composed by response surface analysis. The best campholenic aldehyde selectivity was found to be 85% (5 mg of catalyst, 70 °C, 0.5 h and the use of ethyl acetate as a solvent). Furthermore, the main factors and their combinations that had the greatest significance in the synthesis were adjusted to a polynomial second order model. The factors with the main influence on conversion were the catalyst amount, reaction time, solvent type, and the combined factor between catalyst amount and the solvent type. In the case of campholenic aldehyde selectivity no significant factor was found.
Resumo O catalisador Cu/MCM-41, sintetizado pelo método de impregnação a umidade incipiente, foi caracterizado por DRX, XPS, TPD-NH3 e adsorção-dessorção de N2 e testado na reação de isomerização do epóxido de α-pineno. Diferentes condições de reação foram exploradas a partir de um desenho experimental central composto. A melhor seletividade de aldeído camfolênico encontrada foi de 85% (5 mg de catalisador; 70 °C; 0,5 h e acetato de etilo como solvente). Além disso, os principais fatores e as combinações entre eles que tiveram influência na síntese do aldeído camfolênico foram ajustados a um modelo polinomial de segunda ordem. Verificou-se que os fatores com a principal influência na conversão foram a quantidade de catalisador, o tempo de reação e o tipo de solvente e o fator combinado entre a quantidade de catalisador e o tipo de solvente. No caso da seletividade do aldeído camfolênico, não foi encontrado um fator significativo.
