A Molecular Analogue of the C−H Activation Intermediate of the Silica‐Supported Ga(III) Single‐Site Propane Dehydrogenation Catalyst: Structure and XANES Signature

Recent Progress of Ga-Based Catalysts for Catalytic Conversion of Light Alkanes

The efficient and clean conversion of light alkanes is a research hotspot in the petrochemical industry, and the development of effective and eco-friendly non-noble metal-based catalysts is a key factor in this field. Among them, gallium is a metal component with good catalytic performance, which has been extensively used for light alkanes conversion. Herein, we critically summarize recent developments in the preparation of gallium-based catalysts and their applications in the catalytic conversion of light alkanes. First, we briefly describe the different routes of light alkane conversion. Following that, the remarkable preparation methods for gallium-based catalysts are discussed, with their state-of-the-art application in light alkane conversion. It should be noticed that the directional preparation of specific Ga species, strengthening metal-support interactions to anchor Ga species, and the application of new kinds of methods for Ga-based catalysts preparation are at the leading edge. Finally, the review provides some current limitations and future perspectives for the development of gallium-based catalysts. Recently, different kinds of Ga species were reported to be active in alkane conversion, and how to separate them with advanced in situ and ex situ characterizations is still a problem that needs to be solved. We believe that this review can provide base information for the preparation and application of Ga-based catalysts in the current stage. With these summarizations, this review can inspire new research directions of gallium-based catalysts in the catalysis conversion of light alkanes with ameliorated performances.

A Robust and Efficient Propane Dehydrogenation Catalyst from Unexpectedly Segregated Pt2Mn Nanoparticles

The increasing demand for short chain olefins like propene for plastics production and the availability of shale gas make the development of highly performing propane dehydrogenation (PDH) catalysts, robust toward industrially applied harsh regeneration conditions, a highly important field of research. A combination of surface organometallic chemistry and thermolytic molecular precursor approach was used to prepare a nanometric, bimetallic Pt-Mn material (3 wt % Pt, 1.3 wt % Mn) supported on silica via consecutive grafting of a Mn and Pt precursor on surface OH groups present on the support surface, followed by a treatment under a H₂ flow at high temperature. The material exhibits a 70% fraction of the overall Mn as Mn^II single sites on the support surface; the remaining Mn is incorporated in segregated Pt₂Mn nanoparticles. The material shows great performance in PDH reaction with a low deactivation rate. In particular, it shows outstanding robustness during repeated regeneration cycles, with conversion and selectivity stabilizing at ca. 37 and 98%, respectively. Notably, a material with a lower Pt loading of only 0.05 wt % shows an outstanding catalytic performance─initial productivity of 4523 g_C3H6/g_Pt h and an extremely low k_d of 0.003 h^-1 under a partial pressure of H₂, which are among the highest reported productivities. A combined in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, electron paramagnetic resonance, and metadynamics at the density functional theory level study could show that the strong interaction between the Mn^II-decorated support and the unexpectedly segregated Pt₂Mn particles is most likely responsible for the outstanding performance of the investigated materials.

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

This work explores how H₂ pretreatment at 550 °C induces structural transformation of two gallia-based propane dehydrogenation (PDH) catalysts, viz. nanocrystalline γ/β-Ga₂O₃ and amorphous Ga₂O₃ (GaO_x) supported on silica (γ-Ga₂O₃/SiO₂ and Ga/SiO₂, respectively) and how it affects their activity, propene selectivity and stability with time on stream (TOS). Ga/SiO₂–H₂ shows poor activity and propene selectivity, no coking and no deactivation with TOS, similar to Ga/SiO₂. In contrast, the high initial activity and propene selectivity of γ-Ga₂O₃/SiO₂–H₂ decline with TOS but to a lesser extent than in calcined γ-Ga₂O₃/SiO₂. In addition, γ-Ga₂O₃/SiO₂–H₂ cokes less than γ-Ga₂O₃/SiO₂. Ga K-edge X-ray absorption spectroscopy suggests an increased disorder of the nanocrystalline γ/β-Ga₂O₃ phases in γ-Ga₂O₃/SiO₂–H₂ and the emergence of additional tetrahedral Ga sites (Ga_IV). Such Ga_IV sites are strong Lewis acid sites (LAS) according to studies using adsorbed pyridine and CO probe molecules, i.e., the abundance of strong LAS is higher in γ-Ga₂O₃/SiO₂–H₂ compared to γ-Ga₂O₃/SiO₂ but lower than in Ga/SiO₂ and Ga/SiO₂–H₂. Dissociation of H₂ on the Ga–O linkages in γ-Ga₂O₃/SiO₂–H₂ yields high-frequency Ga–H bands that are observed in Ga/SiO₂ and Ga/SiO₂–H₂ but not detected in γ-Ga₂O₃/SiO₂. We attribute the increased amount of Ga_IV sites in γ-Ga₂O₃/SiO₂–H₂ mostly to an increased disorder in γ/β-Ga₂O₃. X-ray photoelectron spectroscopy detects the formation of Ga⁺ and Ga⁰ species in both Ga/SiO₂–H₂ and γ-Ga₂O₃/SiO₂–H₂. Therefore, it is likely that a minor amount of Ga_IV sites also forms through the interaction of Ga⁺ (such as Ga₂O) and/or Ga⁰ with silanol groups of SiO₂.

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.