One pot synthesis of ultrasmall NiMo catalysts supported on amorphous alumina with enhanced type 2 sites for hydrodesulfurization reaction: A combined experimental and theoretical study

Title : One pot synthesis of ultrasmall NiMo catalysts supported on amorphous alumina with enhanced type 2 sites for hydrodesulfurization reaction: A combined experimental and theoretical study

Abstract:

The deep removal of high molecular weight sulphur compounds (e.g., 4,6, dimethyl dibenzothiophene) is challenging due to their steric hindrance.  Hydrogenation desulfurization (HYD) pathway is the main pathway to remove these sulfur compounds and it is mainly governed by the number of type 2 sites. The formation of type 2 sites can be enhanced by modulating the pore structure and the interaction between the active metal and support. To this end, we report the enhanced HDS catalytic activity of ultrasmall NiMo supported on amorphous alumina (A-Al₂O₃) catalysts by one pot colloidal synthesis method followed by calcination and sulfidation. The amorphous alumina (A-Al₂O₃) was chosen as the support due to its lower surface energy, better physicochemical properties and enhanced acidic sites (due to the dominance of tetra and penta coordinated [Al] sites) than crystalline alumina phase. At 20% metal oxide composition, NiMo supported on A-Al₂O₃ catalyst showed 1.4 and 1.2 times more reaction rate constant and turn over frequency (TOF) respectively than the conventional catalyst (wet impregnated NiMo catalysts) for HDS reaction of dibenzothiophene reactant molecule. A-Al₂O₃ supported catalysts represented enhanced type 2 sites formation (because this catalyst possesses higher sulfidation degree (80%) and NiMoS sites (19.3 x 10¹⁷ sites/mg) with desired optimum stacking degree (2.5) than wet impregnated catalyst at same metal oxide composition 20%) along with higher active metal dispersion, Mo edge site fraction. The experimental observations were also supported by DFT simulations.  Lower heat of adsorption (< 4.2 ev for MoS₂ interaction and < 3.15 ev for Ni doped MoS₂ interaction) values for A-Al₂O₃ confirmed the presence of weaker metal-support interaction in A-Al₂O₃ in contrast to crystalline ?-Al₂O₃. The weak metal-support interaction for prepared catalysts clearly suggests the higher formation of type 2 sites which leads to higher catalytic activity for HDS reaction.

Keywords- Amorphous Alumina, Colloidal, Desulfurization, Metal-support Interaction

Audience take-away:

• As described, A-Al₂O₃ is a better catalytic support than ?-Al₂O₃ so it can be used as a support for other heterogeneous catalysts.
• The developed approach has drastically improved the sulfur removal from petroleum feedstocks.
• The catalyst preparation method is just a one step process that make it easy to handle and increases the reproducibility.

Biography:

Shalini Arora studied at IIT BHU, Varanasi and graduated as M. Tech in 2016. She then joined her PhD in the nanotechnology and catalysis group of Prof. Sri Sivakumar at IIT Kanpur. She has filed an Indian patent based on her PhD thesis work and published articles in reputed journals.