RESUMO

Ni-MoS2/γ-Al2O3 catalysts are commonly used in hydrotreating to enhance fossil fuel quality. The extensive research on these catalysts reveals a gap in understanding the role of Ni, often underestimated as an inactive sulfide phase or just a MoS2 promoter. In this work, we focused on analyzing whether well-dispersed supported nickel nanoparticles can be active in the hydrodesulfurization of dibenzothiophene. We dispersed Ni by Strong Electrostatic Adsorption (SEA) method across four supports with different types of acidity: silica (~ neutral acidity), γ-Al2O3 (Lewis acidity), H+-Y zeolite, and microporous-mesoporous H+-Y zeolite (both with Brønsted-Lewis acidity). Our findings reveal that Ni is indeed active in dibenzothiophene hydrodesulfurization, even with alumina and silica as supports, although their catalytic activity declines abruptly in the first hours. Contrastingly, the acid nature of zeolites imparts sustained stability and performance, attributed to robust metal-support interactions. The efficacy of the SEA method and the added mesoporosity in zeolites further amplify catalytic efficiency. Overall, we demonstrate that Ni nanoparticles may perform as a hydrogenating metal in the same manner as noble metals such as Pt and Pd perform in hydrodesulfurization. We discuss some of the probable reasons for such performance and remark on the role of Ni in hydrotreatment.

RESUMO

Quantification of the gas streams from chemical systems such as catalytic reactors are routinely performed by on-line gas chromatography. Gas chromatographs used for this purpose are typically provided with a combination of thermal conductivity (TCD) and flame ionization (FID) detectors to be able to detect and quantify both permanent gases; COx, N2, H2, etc., and hydrocarbons. However, the accuracy of the quantification is hindered by the intrinsic limitations of each type of detector. Namely, TCD has low sensitivity and FID does not detect permanent gases. Therefore, modern gas chromatographs include methanizer units to partially overcome this shortcoming by converting COx to methane. However, as far as these authors know, the literature has not presented an analytical method to characterize gas streams with high accuracy by the simultaneous use of a combination of a TCD-FID detection system provided with a methanizer. This work is an attempt to solve this problematic; it consists of the formulation of a mathematical model for the well-known external and internal standard quantification methods in gas chromatography. The analysis of the gas stream from a catalytic reactor performing the combustion of methane was used to validate the developed method. The concentration ranges of the analysed gases were: 0.8-7.7 vol% of CH4, CO2, and CO, 7.7-38.5 vol.% of O2, and 46.2-90.8 vol.% of N2 at a total flow of 130 mL min-1. It was found that the commonly applied external standard method leads not only to inaccurate quantification but also to physically meaningless carbon balances and conclusions on the behaviour of the selected model system. In contrast, the internal standard method led to a highly accurate quantification with a physically meaningful carbon balance. Considering these findings, this contribution also draws attention to the need for a thoughtful application of chromatographic methods when studying the reactivity of gas systems.

Assuntos

Cromatografia Gasosa/métodos , Gases/análise , Sistemas On-Line , Carbono/análise , Catálise , Ionização de Chama , Metano/análise , Oxigênio/análise , Padrões de Referência , Reprodutibilidade dos Testes , Condutividade Térmica

RESUMO

Ordered materials with interconnected porosity allow the diffusion of molecules within their inner porous structure to access the active sites located in the microporous core. As a follow-up of our work on engineering of MOF-808, in this contribution, we study the synthesis of defective MOF-808 using two different strategies: the use of modulators and the surfactant-assisted synthesis to obtain materials with ordered and interconnected pores. The results of the study indicated that (i) the use of modulators of different chain length led to the formation of microporous/mesoporous MOFs through the formation of missing linker defects. However, the use of the acetic acid contributes to the formation of MOFs with larger mesoporous size distributions compared to materials synthesized with formic and propionic acids as modulators, and (ii) the self-assembly of CTAB surfactant produced an ordered microporous/macroporous network which enhanced crystallinity. However, the surface properties of the materials seem to be unaffected by the use of surfactants during synthesis. These results contribute to the development of ordered materials with a broad range of pore size distributions and give rise to new opportunities to extend the applications of MOF-808.