Study of the impregnation of NiMo assisted by chelating agents for hydrodesulfurization-supported catalysts over mesopor
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ARTICLE Study of the impregnation of NiMo assisted by chelating agents for hydrodesulfurization-supported catalysts over mesoporous silica Karen A. Beltrán, Lorena Álvarez-Contreras,a) Anabel De la Cruz, and Alfredo Aguilar-Elguezabal Departamento de Ingeniería y Química de los Materiales, Centro de Investigación en Materiales Avanzados S. C. (CIMAV), Chihuahua 31136, Chih, México (Received 15 April 2018; accepted 10 August 2018)
Molybdenum sulfide hydrotreating catalysts promoted with nickel over tridimensional mesoporous silica (KIT-6 post synthesis modified with alumina) were prepared with three different chelating agents. Citric acid and EDTA (ethylenediaminetetraacetic acid) were used as typical chelates and the new suggestion, polyacrylic acid as a polymeric agent. The catalysts were synthesized by the incipient wetness impregnation method, and two different activation methods were applied to determine the correlation between the chelating agent and activation conditions. The beneficial use of chelating agents was evaluated in their performance on HDS (hydrodesulfurization) of DBT (dibenzothiophene). To determine the properties of catalysts, nitrogen physisorption, X-ray diffraction, HRTEM (high-resolution transmission electron microscopy), and TGA (thermogravimetric analysis) were used. The beneficial effect of chelating Ni during impregnation to avoid NiSx formation and thus promoting NiMoS arrangement was clearly observed in the catalytic HDS performance, and the TGA analysis of Ni-chelate complexes also confirms this theory. The catalyst with the best performance in the HDS reaction of DBT was the synthesized with citric acid and a slow rate temperature sulfidation.
I. INTRODUCTION
The increase in fuel demand and the consequently atmospheric pollution growth has induced lower permissible sulfur content in the environmental regulations. Industrially to reach the maximum content of 10 ppm of sulfur on diesel fuels, a catalytic process with high hydrogen pressure is required,1 being this hydrotreating process expensive and of severe conditions. Sulfur removal becomes more complicated due to the high refractory sulfur content of some crude oils such as benzothiophenes and alkyldibenzothiophenes,1 and even more difficult using the same catalyst used since World War I, which normally consists of molybdenum and tungsten sulfides, promoted with elements like nickel or cobalt over alumina as support.2 Nowadays, commercial unsupported catalysts such as NEBULA meet these regulations, but with high costs3; since this catalyst is a trimetallic (NiMoW), it has high density, low surface area, and high cost. In consequence, many of the new research is focused on the development of cheaper catalysts with high surface areas and low and well-dispersed metal loadings. An attractive alternative is the use of the SiO2-based high surface area mesoporous materials, which offers more than 2-fold the surface area of commercial alumina and allows the possibility to a)
Address all correspondence to this author. e-mail: lorena.alvarez@ci
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