CaH2-Assisted Molten Salt Synthesis of Zinc-Rich Intermetallic Compounds of RhZn13 and Pt3Zn10 for Catalytic Selective Hydrogenation Application

Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes

Propane Dehydrogenation on Single-Site [PtZn4] Intermetallic Catalysts

Surface Coordination Decouples Hydrogenation Catalysis on Supported Metal Catalysts

Toward Phase and Catalysis Control: Tracking the Formation of Intermetallic Nanoparticles at Atomic Scale

A novel nanostructured Pd2Ga intermetallic catalyst is presented and compared to elemental Pd and a macroscopic bulk Pd2Ga material concern- ing physical and chemical properties. The new material was prepared by controlled co-precipitation from a single phase layered double hydroxide precursor or hydrotalcite-like compound, of the composition Pd0.025Mg0.675Ga0.3(OH)2(CO3)0.15 ∙ m H2O. Upon thermal reduction in hydrogen, bi- metallic nanoparticles of an average size less than 10 nm and a porous MgO/MgGa2O4 support are formed. HRTEM images confirmed the pres- ence of the intermetallic compound Pd2Ga and are corroborated by XPS investigations which revealed an interaction between Pd and Ga. Due to the relatively high dispersion of the intermetallic compound, the catalytic activity of the sample in the semi-hydrogenation of acetylene was more than five thousand times higher than observed for a bulk Pd2Ga model catalyst. Interestingly, the high selectivity of the model catalysts towards the semi-hydrogenated product of 74% was only slightly lowered to 70% for the nano-structured catalyst, while an elemental Pd reference cata- lyst showed only a selectivity of around 20% under these testing conditions. This result indicates the structural integrity of the intermetallic com- pound and the absence of elemental Pd in the nano-sized particles. Thus, this work serves as an example of how the unique properties of an intermetallic compound, well-studied as a model catalyst, can be made accessible as a real high performing materials allowing establishment of structure-performance relationships and other application-related further investigations. The general synthesis approach is assumed to be applica- ble to several Pd-X intermetallic catalysts for X being elements forming hydrotalcite-like precursors in their ionic form.

The effect of nickel precursors and the temperature annealing to obtain intermetallic Ni3Sn2 alloy catalysts on its activity and selectivity in the selective hydrogenation of biomass-derived furfural (FFald) were investigated. Two types of nickel precursors (c.a., i) nickel metal (Ni°) derived from Raney®nickel and ii) nickel ion (Ni2+) derived from nickel chloride) were employed as the starting materials via hydrothermal at 423 K for 24 h followed by reduction with H2 at the elevated temperature of 573-873 K for 1.5 h. The physico-chemical properties of the intermetallic Ni3Sn2 were characterized by XRD, N2-, and H2-adsorption, ICP-AES, and NH3-TPD. The intermetallic Ni3Sn2 alloy catalysts, both bulk and supported, demonstrated high activity and selectivity towards hydrogenation of FFald. The activity and selectivity of g-Al2O3 and AA-supported Ni3Sn2 alloy catalysts in the hydrogenation of FFald to furfuryl alcohol (FFalc) were maintained even after annealing at up to 873 K, but that of bulk Ni3Sn2 drastically dropped. Ni-Sn alloy catalysts which were obtained from Raney®Ni precursor showed more stable than that of nickel salts during hydrogenation of furfural to furfuryl alcohol. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation, which is currently accomplished by modified palladium catalysts. Herein, we rep...

Supported ordered intermetallic compounds exhibit superior catalytic performance over their disordered alloy counterparts in diverse reactions. But the synthesis of intermetallic compounds catalysts often requires high-temperature annealing that leads to the sintering of metals into larger crystallites. Herein, we report a small molecule-assisted impregnation approach to realize the general synthesis of a family of intermetallic catalysts, consisting of 18 binary platinum intermetallic compounds supported on carbon blacks. The molecular additives containing heteroatoms (that is, O, N, or S) can be coordinated with platinum in impregnation and thermally converted into heteroatom-doped graphene layers in high-temperature annealing, which significantly suppress alloy sintering and insure the formation of small-sized intermetallic catalysts. The prepared optimal PtCo intermetallics as cathodic oxygen-reduction catalysts exhibit a high mass activity of 1.08 A mgPt–1 at 0.9 V in H2-O2 fuel cells and a rated power density of 1.17 W cm–2 in H2-air fuel cells.

Completely or partially ordered intermetallic compounds possess unique electronic structure and chemical bonding, establishing them as an emergent class of catalytic materials for selective hydrogenation reactions. In this review, we focus on the structural and chemical aspects of different classes of intermetallic compounds, followed by illustrative examples highlighting the impact of their structural/chemical features on catalytic hydrogenation. We limit the scope of our discussion to the selective hydrogenation of alkynes (acetylene). We focus our discussion on how the isolation of active sites, formation of defined surface ensembles, partial charge transfer between heteroatoms, and alteration of the surface electronic structure impact activity and selectivity toward the desired product(s), based on recent literature observations. This review contributes to informing the appropriate selection of intermetallic catalysts for hydrogenation reactions to achieve high selectivity.

Platinum-based atomically ordered alloys (i.e., intermetallic compounds) have distinct advantages over disordered solid solution counterparts in boosting the cathodic oxygen-reduction reaction (ORR) in proton-exchange-membrane fuel cells. Nevertheless, the pivotal role of ordering degree of intermetallic catalysts in promoting ORR performance has been ignored heavily so far, probably owing to the lack of synthetic routes for controlling the ordering degree, especially for preparing highly ordered intermetallic catalysts. Herein, a family of intermetallic PtFe catalysts with similar particle size of 3-4nm but varied ordering degree in a wide range of 10-70% are prepared. After constructing the PtFe/Pt core/shell structure with around 3 Pt-layer skin, a positive correlation between the ordering degree of the intermetallic catalysts and their ORR activity and durability is identified. Notably, the highly ordered PtFe/Pt catalyst exhibits a high mass activity of 0.92 A mgPt -1 at 0.9 ViR-corrected as cathode catalyst in H2 -O2 fuel cell, with only 24% loss after accelerated durability tests. The ordering degree-dependent performance can be ascribed to the compressive strain effect induced by the intermetallic PtFe core with smaller lattice parameters, and the more thermodynamically stable intermetallic structure compared to disordered alloys.

Strain engineering has been widely used to optimize platinum-based oxygen reduction reaction (ORR) catalysts for proton exchange membrane fuel cells (PEMFCs). PtM3 (M is base metals), a well-known high-compressive-strain intermetallic alloy, shows promise as a low platinum ORR catalyst due to high intrinsic activity. However, during the alloying of Pt with a threefold amount of M, a notable phase separation between Pt and M may occur, with M particles rapidly sintering while Pt particles grow slowly, posing a challenge in achieving a well-defined PtM3 intermetallic alloy. Here, an entropy-driven Ostwald ripening reversal phenomenon is discovered that enables the synthesis of small-sized Pt(FeCoNiCu)3 intermetallic ORR catalysts. High entropy promotes the thermodynamic driving force for the alloying Pt with M, which triggers the Ostwald ripening reversal of sintered FeCoNiCu particles and facilitates the formation of uniform Pt(FeCoNiCu)3 intermetallic catalysts. The prepared Pt(FeCoNiCu)3 catalysts exhibit a high specific activity of 3.82mAcm-2, along with a power density of ≈1.3Wcm-2 at 0.67V and 94°C with a cathode Pt loading of 0.1mgcm-2 in H2-air fuel cell.

BackgroundIn a routine handling of a catalyst material, exposure to air can usually not be avoided. For noble metal catalysts that are resistant to oxidation, this is not an issue, but becomes important for intermetallic catalysts composed of two or more non-noble chemical elements that possess much different standard enthalpies of the oxide formation. The element with higher affinity to oxygen concentrates on the surface in the oxide form, whereas the element with lower affinity sinks into the subsurface region. This changes the number of active sites and the catalytic performance of the catalyst. We have investigated the instability of the surface composition to oxidation of the Ga3Ni2 noble metal-free intermetallic compound, a new catalyst for the CO2 reduction to CO, CH4 and methanol.MethodsThe instability of the oxidized Ga3Ni2 surface composition to different heating–annealing conditions was studied by X-ray photoelectron spectroscopy (XPS), used to determine the elemental composition and the chemical bonding in the near-surface region. The dispersion of active sites available for the chemisorption of H2 and CO on the Ga3Ni2 catalyst surface was determined by H2 and CO temperature-programmed desorption. CO2 conversion experiments were performed by using the catalyst material reduced in hydrogen at temperatures of 300 and 600 °C.ResultsXPS study of the Ga3Ni2 surface subjected to different heating–annealing conditions has revealed that the concentration of Ga at the oxidized surface is strongly enhanced and the concentration of Ni is strongly depleted with respect to the values in the bulk. By annealing the surface at 600 °C in ultra-high vacuum, the oxides have evaporated and thermal diffusion of atoms near the surface has partially reconstructed the surface composition towards the energetically more favorable bulk value, whereas annealing at a lower temperature of 300 °C was ineffective to change the surface composition. Catalytic tests were in agreement with the XPS results, where an increased CO2 conversion for the catalyst reduced with hydrogen at a higher temperature followed an increased Ni/Ga surface concentration ratio.ConclusionsThe instability of the active surface chemical composition to oxidation in air must be taken into account when considering noble metal-free intermetallic catalysts as alternatives to the conventional catalysts based on noble metals. Ga3Ni2 and other Ga–Ni intermetallic compounds are good examples of binary intermetallic catalysts, whose catalytic performance is strongly affected by exposure to the air.

Self-Assembly Ultrathin Fe-Terephthalic Acid as Synergistic Catalytic Platforms for Selective Hydrogenation

C2H2 selective hydrogenation over the CuxMy or PdxNy intermetallic compounds: The influences of partner metal type and ratio on the catalytic performance

Multi-metal nanoparticles, particularly alloys and intermetallic compounds, are useful catalysts for a variety of chemical transformations. Supported intermetallic nanoparticle catalysts are usually prepared by depositing precursors onto a support followed by high-temperature annealing, which is necessary to generate the intermetallic compound but causes sintering and minimizes surface area. Here we show that solution chemistry methods for converting metal nanoparticles into intermetallic compounds are applicable to supported nanoparticle catalyst systems. Unsupported nanocrystalline Pt can be converted to nanocrystalline PtSn, PtPb, PtBi, and FePt3 by reaction with appropriate metal salt solutions under reducing conditions. Similar reactions convert Al2O3, CeO2, and carbon-supported Pt nanoparticles into PtSn, PtPb, PtSb, Pt3Sn, and Cu3Pt. These reactions generate supported alloy and intermetallic nanoparticles directly in solution without the need for high temperature annealing or additional surface stabilizers. These supported intermetallic nanoparticles are catalytically active for chemical transformations such as formic acid oxidation (PtPb/Vulcan) and CO oxidation (Pt3Sn/graphite). Notably, PtPb/Vulcan XC-72 was found to electrocatalytically oxidize formic acid at a lower onset potential (0.1 V) than commercial PtRu/Vulcan XC-72 (0.4 V).