Atomic Control of Active Site Ensembles in Ordered Alloys to Enhance Hydrogenation Selectivity

Intermetallic compounds offer unique opportunities for atom-by-atom manipulation of catalytic ensembles through precise stoichiometric control. The [Pd, (M), Zn] γ-brass phase allows for controlled synthesis of Pd-M-Pd catalytic sites (M = Zn, Pd, Cu, Ag and Au) isolated in an inert Zn matrix. These multi-atom heteronuclear active sites are catalytically distinct from Pd single atoms and fully coordinated Pd. We quantify the unexpectedly large effect of active site composition (i.e., identity of M atom in Pd-M-Pd sites) on ethylene selectivity during acetylene semi-hydrogenation. Subtle stoichiometric control demonstrates Pd-Pd-Pd sites are active for ethylene hydrogenation, whereas Pd-Zn-Pd sites show no measurable ethylene to ethane conversion. Agreement between experimental and density functional theory predicted activities and selectivities demonstrates precise control of Pd-M-Pd active site composition. The diversity and well-defined structure of intermetallics can be utilized to design active sites assembled with atomic-level precision.

Alkali-Added Catalysts Based on LaAlO3 Perovskite for the Oxidative Coupling of Methane

In this study, we aimed to enhance the catalytic activity of perovskite catalysts and elucidate their catalytic behavior in the oxidative coupling of methane (OCM), using alkali-added LaAlO3 perovskite catalysts. We prepared LaAlO3_XY (X = Li, Na, K, Y = mol %) catalysts and applied them to the OCM reaction. The results showed that the alkali-added catalysts’ activities were promoted compared to the LaAlO3 catalyst. In this reaction, ethane was first synthesized through the dimerization of methyl radicals, which were produced from the reaction of methane and oxygen vacancy in the perovskite catalysts. The high ethylene selectivity of the alkali-added catalysts originated from their abundance of electrophilic lattice oxygen species, facilitating the selective formation of C2 hydrocarbons from ethane. The high COx (carbon monoxide and carbon dioxide) selectivity of the LaAlO3 catalyst originated from its abundance of nucleophilic lattice oxygen species, favoring the selective production of COx from ethane. We concluded that electrophilic lattice oxygen species play a significant role in producing ethylene. We obtained that alkali-adding could be an effective method for improving the catalytic activity of perovskite catalysts in the OCM reaction.

High catalytic performance of Al–Pd–(Ru, Fe) icosahedral approximants for acetylene semi-hydrogenation

The Al–Pd–(Ru, Fe) icosahedral approximants exhibited high catalytic ethylene selectivity and stability for semi-hydrogenation of acetylene.

C-H and C-C bonds activation of propane to propylene and ethylene selectivity assisted by CO2 over titania catalysts

C-H and C-C bonds dissociation over stable titania-based catalysts were studied for propane conversion assisted by CO2 to produce propylene and ethylene. The catalysts were characterized to determine the properties...

Zinc oxide-modified mordenite as an effective catalyst for the dehydrogenation of (bio)ethanol to acetaldehyde

Varying the extraframework metal cation on alkali exchanged mordenite tunes the ethanol dehydrogenation properties of ZnO supported on mordenite, resulting in enhanced lifetime, low ethylene selectivity and increased acetaldehyde productivity per Zn.

The Effect of Shape-Controlled Pt and Pd Nanoparticles on Selective Catalytic Hydrodechlorination of Trichloroethylene

Tailoring the shape of nanoscale materials enables obtaining morphology-controlled surfaces exhibiting specific interactions with reactants during catalytic reactions. The specifics of nanoparticle surfaces control the catalytic performance, i.e., activity and selectivity. In this study, shape-controlled Platinum (Pt) and Palladium (Pd) nanoparticles with distinct morphology were produced, i.e., cubes and cuboctahedra for Pt and spheres and polyhedra/multiple-twins for Pd, with (100), (111 + 100), curved/stepped and (111) facets, respectively. These particles with well-tuned surfaces were subsequently deposited on a Zirconium oxide (ZrO2) support. The morphological characteristics of the particles were determined by high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD), while their adsorption properties were investigated by Fourier transform infrared spectroscopy (FTIR) of CO adsorbed at room temperature. The effect of the nanoparticle shape and surface structure on the catalytic performance in hydrodechlorination (HDCl) of trichloroethylene (TCE) was examined. The results show that nanoparticles with different surface orientations can be employed to affect selectivity, with polyhedral and multiply-twinned Pd exhibiting the best ethylene selectivity.

Selective Hydrogenation of Acetylene to Ethylene Over Nanosized Gold and Palladium Supported Catalysts

Ethylene, the main raw material for polyethylene production, is a by-product produced by thermally decomposing naphtha and it contains a small amount of acetylene. The acetylene reacts as a permanent catalyst poison for the ethylene polymerization catalyst. In this study, we wanted to improve the acetylene conversion and the ethylene selectivity by selective hydrogenation of acetylene for removing acetylene contained in ethylene. Catalyst was prepared by loading nanosized gold (Au) and palladium (Pd) particles on support (Al2O3, TiO2). Deposition order Au and Pd particles was changed. The activity of the catalyst was investigated using a flow-typed fixed bed reactor under atmospheric pressure. Au and Pd particles deposited on TiO2 were oxidized to Au2O3 and PdO due to strong metal support interaction (SMSI). It was considered that the Au/Pd/Al2O3 catalyst was more active than the Pd/Au/Al2O3 catalyst due to the formation of the interface between Au particles and Pd particles (or support). But Pd/Au/Al2O3 catalyst is considered to have poor activity because Pd particles cover part of the interface between Au and the support. Au/Pd/Al2O3 catalyst showed the best catalytic activity, and acetylene conversion and ethylene selectivity were 100% and about 80% at 40 °C, respectively.