45 binary alloys made of platinum and selected 1^st and 2^nd-row transition metal, platinum group or coin metal were synthesized via a scalable laser synthesis method and tested in three industrially relevant testing environments (one DOC, two ASC). Results indicate the highest activity for alloys with oxygen adsorption enthalpies closest to platinum and the highest durability for alloys containing refractory metals.

Abstract

Commercial diesel oxidation catalysis mainly uses monometallic and bimetallic Pt−Pd-based catalysts, but alloying with different elements has rarely been done systematically under industrial testing conditions. 45 binary alloys made of platinum and a selected 1^st and 2^nd-row transition metal, platinum group element, or coin metal were synthesized via a scalable laser synthesis method. Then, catalytic performance and durability were evaluated for one diesel oxidation and two ammonia-slip environments. The results show the highest activity when the adsorption enthalpy of molecular oxygen of the alloy was similar to the value of Pt. Furthermore, the durability of the alloy catalysts was found to increase with the melting point of the 2^nd element Pt was alloyed with, even at molar fractions. Our results further indicate beneficial synergies beyond the binary systems underlining the possibility of further improvements by considering ternary or multinary alloys, which are accessible via laser synthesis.

We explored Pd/hydroxyapatite (Pd/HAP) catalyst for the selective aerial oxidation of biomass derived 1,6-hexanediol (HDO) to adipic acid (AA) at 70 °C in water under base-free conditions using air as an oxidant, where the basicity of support played an important role in tuning the catalyst activity and to achieve high yields of adipic acid with the long-term stability of the Pd/HAP catalyst.

Abstract

Adipic acid (AA), an important precursor to produce nylon-6, nylon-6,6, and polyurethanes, can be synthesized from biomass-derived 1,6-hexanediol (HDO). Herein, we examined the selective oxidation of 1,6-hexanediol to adipic acid over Pd/support (support- Rice husk ash (RHA), TiO₂, C, ZnO, Al₂O₃, La₂O₃, Mg(OH)₂, and hydroxyapatite (HAP)) catalyst in water at 70 °C under base-free conditions. Pd/HAP exhibited high catalytic activity among the catalysts explored, affording adipic acid (AA) selectively in 89 % yield with complete conversion of HDO. Investigating these Pd/support catalysts and several control experiments inferred that the basicity of the HAP support concertedly with Pd nanoparticle participated in achieving efficient aerial oxidation of HDO to AA, and hence avoided the need for any additional base additives. Advantageously, Pd/HAP exhibited high activity for gram-scale reactions and long-term stability during reusing the catalyst for several cycles without any considerable loss in the catalytic activity.

Sustainable higher alcohol production via Fischer-Tropsch synthesis: Syngas derived from biomass, CO₂, H₂O and renewable energy is going to be a centerpiece in sustainable production of fuels and chemicals. Especially, in decentralized plants high-margin products like higher alcohols need to be produced selectively for competitive operation. Herein a cheap and easy-to-scale Fe-based catalyst was developed for this purpose, outperforming the state-of-the-art Fe powder catalysts.

Abstract

For sustainable production of chemicals like hydrocarbons and oxygenates from renewable carbon sources and electricity Fischer-Tropsch synthesis is focused in current research. Aiming for this purpose, the development of supported powdered and shaped catalysts for low-temperature Fischer-Tropsch synthesis of value-added higher alcohols was addressed in this study. Promising support materials like α-Al₂O₃, SiO₂, ZrO₂ and SiC were assessed and the influence of electrochemical promoters on product formation was investigated. The results show an outstanding promoting effect of lithium on conversion and alcohol selectivity. A beneficial synergistic effect occurred for the combination of 1 % Li and Cu each and could be exploited both for supported powdered and shaped catalysts. Furthermore, effects of surface, shape, porosity and Fe content on pellet catalysts were investigated. Exploiting the beneficial effects found, the first monometallic shaped Fe-based catalyst – outperforming the state-of-the-art monometallic Fe powder catalysts in conversion and selectivity – is presented.

Mechanistic investigation: A redox-active azophenolate ligand supported Ni complex has been shown to be instrumental towards olefin hydrogenation following an unconventional pathway. Detailed mechanistic investigation reveals the ligand-radical promoted hydrogenation via discrete one electron pathway.

Abstract

In the borrowing hydrogen catalysis, hydrogenation of an in situ generated imine or olefinic bond is a crucial step. There is a growing body of literature in olefinic hydrogenation promoted by metal hydride of Earth-abundant metals, where radical mechanism is followed. This report presents a thorough study of the mechanistic details of a nickel catalyzed α-alkylation of ketones with secondary alcohols and showcases that the olefinic hydrogenation of an enone happens, completely bypassing the involvement of a metal hydride. This pathway is radical promoted, where a single electron reduction of the substrate olefin and a subsequent hydrogen atom transfer step are most critical. A series of control reactions, detection of critical reaction intermediates, and radical probe experiments provide compelling proofs for such radical-promoted olefinic hydrogenation. The experimental clues, further aided by DFT calculations altogether suggest the precise one-electron chemistry where the involvement of metal-hydride is not required. Notably, the redox non-innocence of the azophenolate backbone, as well as imposed noninnocence of the substrate olefin, when bound to the catalyst molecule makes such mechanism feasible.

The Cover Feature depicts the possible Ni locations on the MgAlO_x/ZrO₂ support and highlights the superior DRM reaction performance of Ni at the heterointerfacial sites. The catalytic behaviors across these diverse Ni positions are metaphorically represented by the thrust of the rockets and the brightness of the Ni particles. In their Research Article, M. M. Montemore, O. M. Gazit and co-worker demonstrate that the heterointerface between a thin MgAlO_x overlayer and the underlying bulk ZrO₂ is the preferred site for Ni particles. The combined results from XPS, DFT, H₂-TPR, TEM, and catalytic studies indicate that the tri-phase boundary among Ni, MgAlO_x, and ZrO₂ offers unique metal-support interactions and enhanced performance in methane dry reforming. More information can be found in the Research Article by M. M. Montemore, O. M. Gazit and co-workers.

The heterointerface between a thin MgAlO_x overlayer and underlying bulk ZrO₂ is identified as a preferred site for Ni particles. The combined results from XPS, DFT, H₂-TPR, TEM and catalytic studies show that this tri-phase boundary between Ni, MgAlO_x, and ZrO₂ provides unique metal-support interactions and advanced performance in methane dry reforming.

Abstract

The catalytic performance of supported metals is greatly influenced by the interaction with the support material. The role of the support becomes even more important when dealing with metal nanoparticles and high reaction temperatures. Herein, we show that interfacial sites between two metal oxides, MgAlO_x and ZrO₂ can bestow high stability as well as enhanced reactivity to nickel (Ni) nanoparticles. We use the MgAlO_x as thin oxides on an underlying bulk ZrO₂. We demonstrate the effect of the metal-support interactions (MSI) in different support locations on the performance in dry reforming of methane (DRM). We find that the rate of DRM catalysis produces a concave-down trend with respect to Ni loading with a maximum at ~0.8–1.1 % wt Ni. Measuring the Ni2p_3/2 binding energy (BE), we find a similar concave-down trend whereas for the Mg2p BE we find a concave-up trend with respect to the Ni loading both with the maximum and minimum centered at 0.8–1.1 % wt Ni, respectively. These trends were correlated with the stability of Ni calculated by DFT. Overall, our results suggest that heterointerfacial sites can be used to tailor moderate MSI, which can be used in the design of DRM catalyst with significantly increased activity and high stability.

Palladium nanoparticles immobilized on porous silica materials have been demonstrated to be efficient heterogeneous catalysts in various coupling and cross-coupling reactions. Utilized in combination with suitable ligands or under ligand-free conditions, these catalysts exhibit high activities and selectivities under mild conditions. Their further advantages include easy handling and recovery, and the possibility of repeated applications.

Abstract

Noble metal nanoparticles supported on porous silica materials represent an important class of heterogeneous catalysts. Recently, a remarkable progress has been made concerning the synthesis, characterization, and catalytic application of noble metal nanoparticles immobilized on zeolites and mesoporous silica-based materials. Various synthesis strategies have been developed, including the application of ligand-assisted metal precursors, multistep synthesis procedures, post-synthetic modifications, and magnetic mesoporous silica particles. Emphasis has been laid on the introduction of green procedures, based on the utilization of environmentally friendly solvents, efficient stabilizing agents, non-toxic reagents, and mild reaction conditions. Palladium nanoparticles have long been recognized as the most efficient catalysts in a wide range of organic transformations, including the Heck, Suzuki, Stille, and Sonogashira reactions. Although these transformations have been extensively investigated in homogeneous catalytic systems, the application of heterogeneous catalysts, including silica-supported Pd⁰ nanoparticles, has gained in increasing importance. This may be due to the easy handling and recovery of the latter catalysts, which facilitates their repeated applications. The aim of this review is to provide an outlook on the current research progress achieved on the development of novel synthetic procedures, affording highly dispersed Pd⁰ nanoparticles immobilized on porous silica materials, which proved to be efficient and recyclable catalysts in C−C coupling and cross-coupling reactions. The focus of this review is on results published in the last six years with a handful of examples in previous years.

A methodology combining EDX analysis and in situ microRaman hyperspectral images has been performed on a mechanical mixture of Pt/CeO₂ and CeO₂ to follow Pt intergranular diffusion during redox treatments. Although platinum diffusion occurs on crystallite surface, intergranular Pt diffusion does not occur at 500 °C. It could be limited by atom trapping on Pt/CeO₂ agglomerates.

Abstract

The dynamics of Pt/CeO₂ catalysts is a hot topic since its knowledge can be used to (re)generate more active sites for redox reactions, even at low temperature (<500 °C). While numerous works focus on the atomic scale, the spatial extent of Pt surface diffusion is poorly known. In this work, it is evaluated at the powder agglomerate scale using an original methodology combining SEM-EDX analysis and in situ optical/microRaman hyperspectral imaging performed on a Pt/CeO₂+CeO₂ mechanical mixture. No intergranular diffusion of platinum during redox cycles at 500 °C is revealed by these techniques, in particular by the Raman images of Ce³⁺ and peroxo species, which are highly sensitive to the presence of Pt atoms. It strongly suggests that Pt surface diffusion takes place only at the nanometer scale and could be limited by atom trapping on Pt/CeO₂ agglomerates. Our method for investigating diffusion processes at the micrometer scale may be extended to other thermochemical conditions and other materials.

A commercial KRED has been immobilized and successfully used as biocatalyst in the asymmetric synthesis of (S)-1-(3,5-bis(trifluoromethyl)phenyl)-ethanol (BTPE), an important intermediate for APIs synthesis. The biotransformations were performed under batch and flow conditions obtaining with most samples the complete conversion after 24 hours and ee >99.9 %. The reusability of immobilized KRED samples has been demonstrated in five consecutive reaction cycles.

Abstract

Both enantiomers of 1-(3,5-bis(trifluoromethyl)phenyl)-ethanol (BTPE) constitute important building-blocks for the synthesis of active pharmaceuticals ingredients (APIs). The reduction of 3’,5’-bis(trifluoromethyl)acetophenone (BTAP) performed with soluble and immobilized ketoreductases (KREDs) can be considered as one of the most efficient routes to produce enantiopure BTPE. In the present work, a commercial KRED was employed as biocatalyst after undergoing immobilization processes and it proved to be extremely efficient in the asymmetric synthesis of (S)-BTPE. The immobilization was studied on a set of different commercially available supports. The best results were obtained with samples immobilized via covalent interaction on short chain amino-functionalized support. Two reaction parameters, temperature, and solvent were optimized in the biocatalytic reduction of BTAP in batch conditions. A 90 : 10 (v/v) 2-propanol (IPA): water solvent system and 30 °C proved to be the best reaction conditions in terms of substrate conversion and easy recovery of the product by simple solvent evaporation. Biotransformations were then performed in a flow system under optimized reaction conditions obtaining with most samples complete conversion after 24 hours and excellent enantiomeric excess (>99.9 %). Finally, the reusability of the immobilized biocatalyst was successfully tested in five consecutive reaction cycles, demonstrating the potential of this approach.