Atomic-scale changes of silica-supported catalysts with nanocrystalline or amorphous gallia phases: implications of hydrogen pretreatment on their selectivity for propane dehydrogenation

Abstract

We explore how H2 pretreatment changes the structure of two gallia-based propane dehydrogenation catalysts, viz. crystalline γ/β-Ga2O3 and amorphous Ga2O3 supported on silica, and how it affects their activity, selectivity and stability on stream.

Combining Atomic Layer Deposition with Surface Organometallic Chemistry to Enhance Atomic-Scale Interactions and Improve the Activity and Selectivity of Cu–Zn/SiO2 Catalysts for the Hydrogenation of CO2 to Methanol

“…XPS experiments were performed to further investigate the state of Zn under (i) reducing conditions, (ii) a CO 2 /H 2 atmosphere, and (iii) methanol vapor. The measurements were performed by treating the passivated catalysts in a reaction chamber connected to the XPS instrument, which allows to study activated materials without their exposure to the ambient air . The Zn 2p 3/2 XPS region of Cu–Zn(5)/SiO 2 after pretreatment in H 2 (300 mbar) at 200 °C (1 h) features a broad peak, indicating the presence of both Zn 0 and Zn 2+ states (Figure b).…”

“…The measurements were performed by treating the passivated catalysts in a reaction chamber connected to the XPS instrument, which allows to study activated materials without their exposure to the ambient air. 49 The Zn 2p 3/2 XPS region of Cu−Zn(5)/SiO 2 after pretreatment in H 2 (300 mbar) at 200 °C (1 h) features a broad peak, indicating the presence of both Zn 0 and Zn 2+ states (Figure 3b). Peak deconvolution yields a Zn 0 /Zn 2+ ratio of 0.45, which is higher than that of Zn(5)/SiO 2 pretreated under identical conditions (Zn 0 /Zn 2+ = 0.36, Figure S43).…”

Reversible transformation of sub-nanometer Ga-based clusters to isolated [4]Ga(4Si) sites creates active centers for propane dehydrogenation

“…In contrast, the more active sites in unsupported nanoparticle catalysts such as β-Ga 2 O 3 or mixed oxide (Ga,Al) 2 O 3 are weak Lewis acid sites (LAS), yet a higher relative amount of mild LAS in those catalysts also leads to increased amounts of coking. [22][23][24][25] Here, we report that ALD-made [4] Ga (Si/Ga) and [5] Ga (Si/Ga) sites on dehydroxylated silica transform, upon contact with ambient air, to [4] Ga (Ga) and [6] Ga (Ga) sites that are contained in ca. sub-nanometer Ga x O y (OH) z clusters that feature no diffraction peaks and are not-discernable by highresolution TEM.…”

“…In contrast, the more active sites in unsupported nanoparticle catalysts such as β-Ga 2 O 3 or mixed oxide (Ga,Al) 2 O 3 are weak Lewis acid sites (LAS), yet a higher relative amount of mild LAS in those catalysts also leads to increased amounts of coking. 22–25…”

Morphology Effect of ZrO2 on Tuning the C–H Bond Activation in Propane Dehydrogenation

“…Developing alternative environmentally friendly and cost-effective PDH catalysts is significant to enhance propene production. It is reported in the literature that metal (Pd, − Ru − ) and metal oxide (GaO x , , ZnO x , , CoO x , VO x , , ZrO x ) based materials are two main PDH catalysts and have been extensively studied. Most of the above active components have to be loaded on a specific matrix to realize a higher dispersion for obtaining a satisfying catalytic performance.…”