Spillover
is a well-known phenomenon in heterogeneous catalysis
and is involved in many important reactions. The establishment of
the spillover concept opened up a new research field for an in-depth
understanding of the dynamic behavior of migrated species on a catalyst
surface. However, a comprehensive understanding of spillover remains
lacking. In recent years, the development of advanced characterization
techniques in combination with well-controlled synthesis methodologies
has provided us with increasing worthwhile information about spillover.
This Review mainly describes recent progress on the characterization
and mechanism of hydrogen spillover and how to effectively utilize
the spillover effect for enhanced catalytic performance. Additionally,
the challenges remaining in this research area are discussed, and
possible research directions for the future are proposed.
In situ tuning of the electronic structure of active sites is a long-standing challenge. Herein, we propose a strategy by controlling the hydrogen spillover distance to in situ tune the electronic structure. The strategy is demonstrated to be feasible with the assistance of CoOx/Al2O3/Pt catalysts prepared by atomic layer deposition in which CoOx and Pt nanoparticles are separated by hollow Al2O3 nanotubes. The strength of hydrogen spillover from Pt to CoOx can be precisely tailored by varying the Al2O3 thickness. Using CoOx/Al2O3 catalyzed styrene epoxidation as an example, the CoOx/Al2O3/Pt with 7 nm Al2O3 layer exhibits greatly enhanced selectivity (from 74.3% to 94.8%) when H2 is added. The enhanced selectivity is attributed to the introduction of controllable hydrogen spillover, resulting in the reduction of CoOx during the reaction. Our method is also effective for the epoxidation of styrene derivatives. We anticipate this method is a general strategy for other reactions.
The contribution of the reverse spillover effect to hydrogen generation reactions is still controversial. Herein, the promotion functions for reverse spillover in the ammonia borane hydrolysis reaction are proven by constructing a spatially separated NiO/Al2O3/Pt bicomponent catalyst via atomic layer deposition and performing in situ quick X-ray absorption near-edge structure (XANES) characterization. For the NiO/Al2O3/Pt catalyst, NiO and Pt nanoparticles are attached to the outer and inner surfaces of Al2O3 nanotubes, respectively. In situ XANES results reveal that for ammonia borane hydrolysis, the H species generated at NiO sites spill across the support to the Pt sites reversely. The reverse spillover effects account for enhanced H2 generation rates for NiO/Al2O3/Pt. For the CoOx/Al2O3/Pt and NiO/TiO2/Pt catalysts, reverse spillover effects are also confirmed. We believe that an in-depth understanding of the reverse effects will be helpful to clarify the catalytic mechanisms and provide a guide for designing highly efficient catalysts for hydrogen generation reactions.
With the ever-increasing awareness of environmental problems, the use of green reaction medium in chemical processes has become an urgent research topic for green and sustainable chemistry. Developing excellent catalytic...
Hydrogen migration from metal particles to the support, known as hydrogen spillover, has provided insights for designing highly efficient catalysts in catalytic processes involving hydrogen. A facile and controllable strategy is highly desired to achieve an effective hydrogen spillover effect on nonreducible oxides for catalytic performance optimization and clarifying the catalytic function of hydrogen spillover. Here, we provide an organic molecular decoration (OMD) strategy obtained by the molecular layer deposition-like pulse method for facilitating hydrogen spillover over the nonreducible silica support. After decorating with the fluoroalkylsilane (FAS) molecular layer, the hydrogen spillover effect over the catalysts (xFAS-Pt/SBA-15) is greatly enhanced due to the presence of carbonaceous species compared with the original Pt/SBA-15. The amount of hydrogen spillover can also be precisely regulated by controlling the FAS pulse number. For cinnamaldehyde hydrogenation, xFAS-Pt/SBA-15 presents superior catalytic performance versus its untreated counterpart and the sample decorated via the traditional method. Also, the catalytic activity varies based on the FAS pulse number, showing a linear correlation with the amount of hydrogen spillover. The altered adsorption behavior of the reactant plays an important role in the hydrogenation selectivity. This facile OMD strategy for efficient hydrogen spillover is general and may have potential applications in many heterogeneous reactions.
A carbon-assisted thermal treatment strategy is introduced to create rich platinum−oxygen vacancy interfacial sites in TiO2 nanotube confined Pt-based catalysts due to reducibility of carbon at high temperature. Compared with...
The rational synthesis of catalysts with controllable
structures
and the study of their structure–activity relationships to
break the limitations of traditional catalysts remain challenging.
Herein, tetrakis(dimethylamido)tin (TDMASn) exposures were used to
modify silicalite-1 (S-1) lacking suitable chemisorption sites on
their surfaces to provide Pt nucleation sites, obtaining a Pt/20TDMASn/S-1
sample. For comparison, Pt species supported on bare S-1 (Pt/S-1)
and Pt species supported on the S-1 of pre-deposited SnO2 (Pt/20SnO2/S-1) were also prepared. Catalysts were characterized
extensively by X-ray diffraction, temperature-programmed reduction,
transmission electron microscopy, X-ray photoelectron spectroscopy,
and diffuse-reflectance infrared Fourier transform spectroscopy of
adsorbed CO. The results showed that this surface modification (TDMASn
or SnO2) yielded up to about a 40-times increase in Pt
content after 20 cycles of Pt atomic layer deposition (ALD). Compared
with Pt/20SnO2/S-1, Pt/20TDMASn/S-1 had a smaller particle
size, stronger interactions between the metal species and the support,
and a lower Sn0 content, thus resulting in a remarkably
higher initial propane conversion in the propane dehydrogenation (PDH)
reaction. The catalytic activity could also be optimized based on
the number of ALD-TDMASn exposures. As a consequence, Sn not only
provided nucleation sites for Pt but also acted as a promoter to enhance
the catalyst performance. This fundamental understanding will help
researchers obtain suitable catalysts for PDH processes.
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