Selective atomic layer deposition of NiO on MoOx/γ-Al2O3 to enhance the active catalytic phase formation for hydrodesulfurization of dibenzothiophene

Abstract

It is well-established that the Ni-decorated MoS2 edge sites (NiMoS) on the γ-Al2O3 surface are the favorable active sites for efficient hydrodesulfurization (HDS). The intimate contact of Ni with MoOx on γ-Al2O3 (under moderate interaction with γ-Al2O3) enhances the reducibility and sulfidability of NiMo catalyst and their HDS activity, consequently. In this work, selective atomic layer deposition (S-ALD) was utilized as an efficient synthesis technique to selectively deposit NiO on MoOx/γ-Al2O3 to enhance the desired NiMoS active catalytic phase formation after sulfidation. The appropriate ALD temperature window for Ni S-ALD was determined between 150 and 180 °C. The prepared catalysts were characterized by NH3-TPD, H2-TPR, XRD, HR-TEM, and XPS. The results supported the selective deposition of NiO on MoOx/γ-Al2O3 but not on the γ-Al2O3 surface. The S-ALD catalysts enhanced the HDS conversions at lower reaction temperatures and pressures compared to their equivalents made by conventional impregnation. At lower pressures, the S-ALD catalysts resulted in up to 52% higher conversions than their corresponding impregnation ones. The study of catalysts surface by HR-TEM and XPS showed that the main reason for enhanced S-ALD catalysts activity is the formation of more active NiMoS desired catalytic phase with more sulfidability than their counterparts made by impregnation.