Title : Hydrodeoxygenation of triglycerides/fatty acid over supported metal catalysts for the production of green diesel
Abstract:
The hydrodeoxygenation (HDO) of stearic acid to produce green diesel has been studied over alumina supported NiMo, and CoMo catalysts. The alumina supported NiMo and CoMo is a potential alternative to the precious metal catalysts for hydrodeoxygenation of stearic acid (C18:0 acid) for the production of diesel-range hydrocarbons. The mole ratio of metals in a bimetallic catalyst plays an extremely vital role in the formation of various catalytically active species. This study thus aims to ascertain the role of Ni/Mo and Co/Mo mole ratio on the performance of NiMo and CoMo catalysts for the HDO of C18:0 acid. The NiMo and CoMo catalysts showed superior catalytic activity compared to Ni and Co catalyst due to the synergistic effect and formation of catalytically superior NiMo and CoMo alloy. The calcined NiMo and CoMo catalysts showed the presence of Ni, Mo, Co, and mixed metal oxide depending on the relative content of metals. Both Ni and NiMo alloy coexist in the NiMo catalysts depending on the Ni and Mo content. With increasing Ni/Mo (mole), the NiMo alloy content in the catalyst increases with the simultaneous decrease in the Ni content. The activity of NiMo catalysts thus enhances with increasing Ni/Mo (mole). The reaction follows a decarbonylation route over Ni sites and a HDO route over NiMo alloy species. C17 and C18 alkanes are thus observed as the dominating hydrocarbon product over Ni and NiMo alloy-rich catalysts, respectively. For 4.1 mmol of metals per g of alumina, Mo and Co oxides were increased with increasing Mo and Co content in the catalysts, respectively. The CoMoO4 was increased with increasing Mo content up to 2.4 mmol Mo only. On the other hand, the reduced CoMo catalysts were gradually enriched with CoMo alloy with increasing Co content up to 2.4 mmol Co and slightly declined for 3.1 mmol Co. The catalytic activity of CoMo catalysts was thus enhanced with increasing Co content. The reaction follows the HDO mechanism over CoMo alloy and reducible Co oxide species. The C18 alkane was thus formed as the dominating hydrocarbon product over CoMo catalysts. The selectivity to C18 alkane was also enhanced with increasing Co content up to up to 2.4 mmol Co due to the enrichment of CoMo alloy in the catalyst. The catalytic activity of CoMo catalysts was further enhanced with increasing reaction temperature and metals loading without affecting the selectivity to alkanes much. A suitable kinetic model was also developed to correlate the experimental data.
