The effect of starch addition on combustion synthesis of NiMo–Al2O3 catalysts for hydrodesulfurization

• NiMo–Al2O3 catalysts were prepared by combustion synthesis using starch as fuel.
• The textural properties of the catalysts depended strongly on the starch addition.
• Starch addition markedly improved the sulfidity and generated Ni–Mo–S Type II phase.
• TOF increased with increasing starch addition.
• A starch addition ratio of 2.5 exhibited the best hydrodesulfurization performance.

The effect of starch addition on the precursor combustion reaction, physicochemical properties, active phase, and intrinsic hydrodesulfurization activity of Al2O3-supported Ni–Mo catalysts prepared by combustion synthesis in a one-pot process has been studied. The results show that the increase in starch addition markedly enhances the molar enthalpy of the combustion reaction, develops the porosity of the catalysts, and improves the reducibility and sulfidability by reducing the interaction of Mo and Ni with the Al2O3 support. Thus, the total number of Ni–Mo–S active sites increases, and substantial amounts of the Ni–Mo–S Type II phase forms, leading to an increase in the turnover frequency (TOF) for the catalysts. However, excess starch will lead to a large agglomeration of Mo particles, resulting in high MoS2 stacking and low MoS2 dispersion. As a result, the specific activities of hydrodesulfurization over NiMoAl-x catalysts peak at a starch addition ratio (x) of 2.5 ((C6H10O5):2Al).

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