Direct conversion of methane to aromatics and hydrogen via a heterogeneous trimetallic synergistic catalyst

Non-oxidative methane dehydro-aromatization reaction can co-produce hydrogen and benzene effectively on a molybdenum-zeolite based thermochemical catalyst, which is a very promising approach for natural-gas upgrading. However, the low methane conversion and aromatics selectivity and weak durability restrain the realistic application for industry. Here, a mechanism for enhancing catalysis activity on methane activation and carbon-carbon bond coupling has been found to promote conversion and selectivity simultaneously by adding platinum-bismuth alloy cluster to form a trimetallic catalyst on zeolite (Pt-Bi/Mo/ZSM-5). This bimetallic alloy cluster has synergistic interaction with molybdenum: the formed CH3* from Mo2C on the external surface of zeolite can efficiently move on for C-C coupling on the surface of Pt-Bi particle to produce C2 compounds, which are the key intermediates of oligomerization. This pathway is parallel with the catalysis on Mo inside the cage. This catalyst demonstrated 18.7% methane conversion and 69.4% benzene selectivity at 710 °C. With 95% methane/5% nitrogen feedstock, it exhibited robust stability with slow deactivation rate of 9.3% after 2 h and instant recovery of 98.6% activity after regeneration in hydrogen. The enhanced catalytic activity is strongly associated with synergistic interaction with Mo and ligand effects of alloys by extensive mechanism studies and DFT calculation.

Exploring the slow-light effect of Pt/TiO2-SiO2 inverse opal on photocatalytic nonoxidative coupling of methane

The slow-photon effect of Pt/TiO₂-SiO₂ inverse opal on photocatalytic nonoxidative coupling of methane was explored regarding the cavity size and filming treatment. The ethane production rate was maximized to 72 μmol g^-1 h^-1 on a filmed microarray with a macroporous diameter of 170 nm, demonstrating the significance of enhancing light-matter interaction for methane conversion.

Doubly Decorated Platinum-Gallium Intermetallics as Stable Catalysts for Propane Dehydrogenation

Propane dehydrogenation (PDH) is a promising chemical process that can satisfy the increasing global demand for propylene. However, the Pt-based catalysts that have been reported thus far are typically deactivated at ≥600 °C by side reactions and coke formation. Thus, such catalysts possess an insufficient life. Herein, we report a novel catalyst design concept, namely, the double decoration of PtGa intermetallics by Pb and Ca, which synergize the geometric and electronic promotion effects on the catalyst stability, respectively. Pb is deposited on the three-fold Pt₃ sites of the PtGa nanoparticles to block them, whereas Ca, which affords an electron-enriched single-atom-like Pt₁ site, is placed around the nanoparticles. Thus, PtGa-Ca-Pb/SiO₂ exhibits an outstandingly high catalytic stability, even at 600 °C (k_d =0.00033 h^-1 , τ=3067 h), and almost no deactivation of the catalyst was observed for up to 1 month for the first time.

Binary and ternary Pt-based clusters grown in a plasma multimagnetron-based gas aggregation source: electrocatalytic evaluation towards glycerol oxidation

Platinum (Pt), platinum-bismuth (PtBi), platinum-copper (PtCu) and platinum-bismuth-copper (PtCuBi) clusters were grown in a gas aggregation source (GAS) equipped with three in-plane plasma magnetrons located in a single region of the gas aggregation zone. The X-ray diffraction results have shown that PtCu clusters form alloys as the decrease of the lattice parameter occurs when the Cu atomic content increases. PtBi clusters do not form alloys, but the presence of secondary Bi oxide phases was detected. Scanning transmission electron microscope mapping images revealed that simultaneously adding Bi and Cu to Pt leads to PtCu alloyed clusters decorated with Bi or CuBi species on the surface. The electrochemical results indicated that the shell might be composed of a metastable CuBi phase. Electrochemical measurements have shown that the addition of Bi or Cu to the Pt clusters enhances the catalytic activity for glycerol oxidation by decreasing the oxidation onset potential.

Metal-based catalysts for the non-oxidative dehydrogenation of light alkanes to light olefins

This review provides an overview of metal-based catalysts, including Pt-, Pd-, Rh- and Ni-based bimetallic catalysts for non-oxidative dehydrogenation of light alkanes to olefins.

Structural trends in the dehydrogenation selectivity of palladium alloys

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd₃M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd₃M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity.

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior.

The effect of strong metal–support interaction (SMSI) on Pt–Ti/SiO2 and Pt–Nb/SiO2 catalysts for propane dehydrogenation

The selectivity of Pt NP's (gray) are modified by SMSI oxides (red) leaving exposed small ensembles capable of dehydrogenation, but with limited activity for hydrogenolysis.

Diffusion-Limited Formation of Nonequilibrium Intermetallic Nanophase for Selective Dehydrogenation

Nonequilibrium intermetallic phases in the nanoscale were realized by diffusion-controlled solid-state transformation, forming SiO₂ supported NPs with Pd core and a CsCl type Pd₁M₁ shell, where M is Sn or Sb. The core-shell geometry is identified from scanning transmission electron microscopy and infrared spectroscopy and the crystal structure is confirmed from in situ synchrotron X-ray diffraction and X-ray absorption spectroscopy. The highly symmetric Pd₁M₁ intermetallic phase has not been reported previously and contains catalytic ensembles with high selectivity toward dehydrogenation of propane. The kinetically limited solid-state reaction is generally applicable to nanoparticle synthesis and could produce materials with desired structures and properties beyond conventional structural limits.