Deactivation of Pt/KL catalyst during n-heptane aromatization reaction

Bimetallic Sites for Catalysis: From Binuclear Metal Sites to Bimetallic Nanoclusters and Nanoparticles

Heterogeneous bimetallic catalysts have broad applications in industrial processes, but achieving a fundamental understanding on the nature of the active sites in bimetallic catalysts at the atomic and molecular level is very challenging due to the structural complexity of the bimetallic catalysts. Comparing the structural features and the catalytic performances of different bimetallic entities will favor the formation of a unified understanding of the structure-reactivity relationships in heterogeneous bimetallic catalysts and thereby facilitate the upgrading of the current bimetallic catalysts. In this review, we will discuss the geometric and electronic structures of three representative types of bimetallic catalysts (bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles) and then summarize the synthesis methodologies and characterization techniques for different bimetallic entities, with emphasis on the recent progress made in the past decade. The catalytic applications of supported bimetallic binuclear sites, bimetallic nanoclusters, and nanoparticles for a series of important reactions are discussed. Finally, we will discuss the future research directions of catalysis based on supported bimetallic catalysts and, more generally, the prospective developments of heterogeneous catalysis in both fundamental research and practical applications.

Insight into different performance of Pt/KL catalysts for n-alkane (C6-C8) aromatization: catalytic role of zeolite channels

Zeolite channel architecture was vital to catalytic activity and products distribution during the naphtha reforming, which could be effectively utilized by designing the locations of active sites. Herein, uniformly dispersed...

Atomic-Scale Designing of Zeolite Based Catalysts by Atomic Layer Deposition

Zeolite-supported catalysts have been widely used in the field of heterogeneous catalysis. Atomic-scale governing the metal or acid sites on zeolites still encounters great challenge in controllable synthesis and developing of novel catalysts. Atomic layer deposition (ALD), owing to its unique character of self-limiting surface reactions, becomes one of the most promising and controllable strategies to tailor the metallic deposition sites in atomic scale precisely. In this review, we present a comprehensive summary and viewpoint of recent research in designing and engineering the structural of zeolite-based catalysts via ALD method. A prior focus is laid on the deposition of metals on the zeolites with emphasis on the isolated states of metals, followed by introducing the selected metals into channels of zeolites associates with identifying the location of metals in and/or out of the channels. Subsequently, detailed analysis of tailoring the acid sites of different zeolites is provided. Assisted synthesis of zeolite and the regioselective deposition of metal on special sites to modify the structures of zeolites are also critically discussed. We further summarize the challenges of ALD with respect to engineering the active sites in heterogeneous zeolite-based catalysts and provide the perspectives on the development in this field.

Highly Selective Aromatization of Octane over Pt-Zn/UZSM-5: The Effect of Pt-Zn Interaction and Pt Position

The effects of Zn-Pt interaction and Pt dispersion over a uniform compact cylindrical shape ZSM-5 (UZSM-5) on the catalytic octane aromatization performance are investigated. The comparison between different Pt- and Zn-modified ZSM-5 catalysts demonstrates the significance of ZSM-5 morphology and, more importantly, the metal distributions on it. For the UZSM-5 support, Pt atoms prefer to occupy the sites within its inner pores, resulting in high selectivity to xylenes during the octane aromatization. The Zn deposit in inner pores and higher dispersion of Pt lead to the spillover of Pt sites to the external surface, which is critical for the activation of octane to produce reaction intermediates that are further converted to aromatics over the inner pore catalytic sites. These effects are evidenced by a diffuse reflection infrared Fourier transform spectroscopy study of CO adsorbed on the catalyst surface. In situ X-ray absorption fine structure spectra are collected to probe the coordination number and the chemical environment of Pt and Zn atoms in the catalysts during the octane aromatization reaction. Pt and Zn are well dispersed and stable during the reaction, and a partial reduction of Pt during the reaction is observed. A theoretical study using the density functional theory method predicts that the reaction and transition-state intermediates upon octane activation are better stabilized by Pt(111) of Pt external surface sites with a smaller activation barrier, indicating their significance in C-H activation. This hypothesis is further evidenced by comparing the octane aromatization performance of various modified catalysts through varying Zn loading, blocking inner pores, and covering the external catalytic sites with SiO₂.

Highly Dispersed Single-Atom Pt and Pt Clusters in the Fe-Modified KL Zeolite with Enhanced Selectivity for n-Heptane Aromatization

Conversion of straight-chain paraffins into aromatics is particularly attractive but extremely challenging in the oil refining industry. Constructing the Pt-supported catalysts with high aromatic selectivity is vital. Here, we report a strategy to use Fe-modified KL zeolites to improve the Pt atom utilization efficiency and anchor them inside KL zeolite channels via atomic-layer deposition technique. A combination of highly dispersed single-atom Pt and electron-rich Pt clusters is fabricated on the KL zeolite through the creation of proper nucleation sites. The resulted catalyst (PtFe-1/KL) exhibits excellent performance for the n-heptane aromatization (90.1% aromatic selectivity) with an apparent activation energy of 131 kJ/mol and much enhanced stability at a relatively lower temperature (420 °C). Experimental analysis and density functional theory calculation demonstrate that the single-atom Pt might play a key role in the initial dehydrogenation of n-heptane to 1-heptene, and the superior stable Pt clusters encapsulated inside Fe-decorated KL zeolite channels accelerate the 1-heptene dehydrocyclization to aromatics. The synergetic interaction between single-atom Pt and Pt clusters enables the PtFe-1/KL catalyst to be one of the most effective n-heptane aromatization catalysts reported to date.

Investigation of the effects of phosphorus on the selective hydrodeoxygenation of anisole over an Fe/SiO2 catalyst

Hydrodeoxygenation (HDO) of lignin derivatives offers an effective approach to produce aromatics.

Boosting Electrochemical Hydrogen Evolution of Porous Metal Phosphides Nanosheets by Coating Defective TiO2 Overlayers

Nonprecious transition metal phosphides (TMPs) have emerged as robust electrocalysts for the hydrogen evolution reaction (HER). However, the TMPs suffer from low activity for water dissociation, which greatly limits the efficiency for alkaline HER. Here, a facile yet robust strategy is reported to boost the HER of metal phosphides by coating defective TiO₂ overlayers. The oxygen vacancies (O_v ) on defective TiO₂ overlayers are found to possess high activity for adsorption and dissociation of water, thereby significantly promoting the initial Volmer step of HER to generate the reactive hydrogen atoms. Moreover, the porous (Co, Ni)₂ P (i.e., Co₂ P and Ni₂ P) nanosheets provide enough active sites for adsorption and recombination of reactive hydrogen atoms to produce hydrogen gas. The catalytic synergy of (Co, Ni)₂ P and O_v coupled with the hierarchically porous structure renders the porous (Co, Ni)₂ P@0.1TiO₂ nanosheet arrays excellent electrocatalysts for HER, showing a small overpotential (92 mV) to yield a current density of 10 mA cm^-2 , a small Tafel slope (49 mV dec^-1 ), and an outstanding stability. This work demonstrates a surface decoration route for enhancing the activity of nonprecious metal-based electrocatalysts for HER.

Synthesis of nano-sized LTL zeolite by addition of a Ba precursor with superior n-octane aromatization performance

Nano-sized LTL zeolites obtained by the Ba-assisted method show improved catalytic performance in n-octane aromatization reaction.