Citric acid-assisted synthesis of γ-alumina-supported high loading CoMo sulfide catalysts for the hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) reactions

Abstract

In the present work, the effect of the citric acid (i.e., adsorption-assisting agent) and the thermal treatment over the citric acid-synthesized CoMo catalyst precursors were investigated. The catalysts were prepared by wet coimpregnation of c-alumina extrude with citric acid-containing CoMo aqueous solution in acid medium (pH = 2-3) and treated at various temperatures (typically between 110 and 400°C) in an air atmosphere. The calumina-supported CoMo sulfide catalysts were evaluated using two different feeds (a model feedstock containing various S and N compounds (hereafter feed 1) and a real feedstock (hereafter feed 2). It was found that the synthesis of alumina-supported high loading CoMo catalyst precursor by wet co-impregnation using citric acid as chelating agent in the CoMo impregnation solution takes place mainly through the uniform deposition-precipitation of Co aqueous complex and Mo citrate onto alumina. This process leads to the formation of nanodispersed Co and Mo species that effectively mitigate the formation of b-CoMoO 4 during the thermal treatment at high temperature (i.e., 350°C). The decomposition reaction of Co aqueouscomplex and Mo citrate deposited on alumina started at 220°C. The gradual degradation of the whole metal citrate with increasing treatment temperature decreased the catalyst activity because of the apparent formation of poorly reducible mixed-metal oxides in the catalyst precursor. The use of citric acid to synthesize the CoMo formulations enhances not only the C-S bond scission through the direct desulfurization pathway, but also the hydrogenation route.

Reactivity of sulfur compounds in FCC decant oils for hydrodesulfurization over CoMoS2/Al2O3 catalysts

“…Moreover, the location of Co species that is known to be anchored on the lateral sites of MoS 2 slabs is of great importance in the formation of the active Co-Mo-S phase. In preparing a highly active CoMoS catalyst, the effect of citric acid (CA) addition on the HDS was well established in previous studies [26][27][28][29]. The addition of CA plays a crucial role in the formation of the Co-Mo-S phase and is also known to affect the slab size and stacking number of CoMoS 2 catalysts [21,23,29].…”

“…Over the past few decades, many researchers have continued to study catalysts that have enhanced the performance and stability of CoMo and NiMo sulfides [17][18][19]. More recently, the addition of citric acid in the preparation of the catalysts has shown much improvement in the catalytic activity in the HDS [20][21][22][23][24][25][26][27][28][29]. CA acts as a chelating agent and has attracted much attention due to its low cost and high solubility compared to other organic additives having similar effects on delaying the sulfidation of Co or Ni species to enable the decoration [19,21].…”

“…As such, the various effects of CA on the supported CoMo catalyst have been reported for many years. However, most of the studies usually were applied to the HDS of model S feeds [20][21][22][23] or middle distillate feedstocks [24][25][26][27][28]. In this work, the S compounds in FCC-DO were carefully analyzed, and the effect of CoMo-CA catalyst on the reactivity of the S compounds in the HDS was investigated.…”

Sustainable development and enhancement of cracking processes using metallic composites

“…Crucial emissions of NO x , SO x , CO x , and particulate matter are the sources of the majority concern for environmental pollution [36]. To reduce their effect, stringent environmental restrictions have been launched in many developed countries across the globe to decrease the sulphur and aromatic contents in automobile fuels aimed at reducing harmful exhaust emissions and improving the quality of air [37].…”

“…However, the design of improved catalysts for hydrotreatment is of predominant importance not only in the reduction of environmental pollution but also in process optimization for feedstocks of low grade [37]. The research and development circle has greeted these challenges with the Fig.…”