Chemoselective hydrogenation of α,β-unsaturated aldehydes on hydrogenated MoOx nanorods supported iridium nanoparticles

High-Density Formation of Ir/MoOx Interface through Hybrid Clustering for Chemoselective Nitrostyrene Hydrogenation

To form high-density metal/oxide interfacial active sites, we developed a catalyst preparation method based on hybrid clustering. An iridium-molybdenum (Ir-Mo) hybrid clustering catalyst was prepared by using the hybrid cluster [(IrCp*)4Mo4O16] (Cp* = η5-C5Me5) as the precursor. The Ir-Mo hybrid clustering catalyst selectively reduced the nitro group in the hydrogenation of 4-nitrostyrene, whereas the coimpregnated Ir-Mo catalyst reduced both the nitro and vinyl groups nonselectively. The hybrid clustering catalyst also exhibited high selectivity, even at a high Ir loading (5 wt %), in contrast to Ir/MoO3, which exhibited high selectivity only at low Ir loadings (<0.3 wt %). In situ X-ray absorption spectroscopy analysis revealed that oxygen vacancies were formed at the Ir/MoOx interface in the presence of H2. We concluded that a high-density Ir/MoOx interface contributes to the preferential adsorption of nitro groups on vacant sites, promoting the selective hydrogenation of nitro groups.

Promoting Amination of Furfural to Furfurylamine by Metal-Support Interactions on Pd/MoO3-x Catalysts

The reductive amination of carbonyl compounds is one of the most straightforward protocols to construct C-N bonds, but highly desires active and selective catalysts. Herein, Pd/MoO3-x catalysts are proposed for furfural amination, in which the interactions between Pd nanoparticles and MoO3-x supports can be easily ameliorated by varying the preparation temperature toward efficient catalytic turnover. Thanks to the synergistic cooperation of MoV -rich MoO3-x and highly dispersed Pd, the optimal catalysts afford the high yield of furfurylamine (84 %) at 80 °C. Thereinto, MoV species not only acts as the acidic promoter to facilitate the activation of carbonyl groups, but also interacts with Pd nanoparticles to promote the subsequent hydrogenolysis of Schiff base N-furfurylidenefurfurylamine and its germinal diamine. The good efficiency of Pd/MoO3-x within a broad substrate scope further highlights the key contribution of metal-support interactions to the refinery of biomass feedstocks.

Highly Efficient Selective Hydrogenation of Cinnamaldehyde to Cinnamyl Alcohol over CoRe/TiO2 Catalyst

Allylic alcohols typically produced through selective hydrogenation of α,β-unsaturated aldehydes are important intermediates in fine chemical industry, but it is still a challenge to achieve its high selectivity transformation. Herein, we report a series of TiO₂-supported CoRe bimetallic catalysts for the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) using formic acid (FA) as a hydrogen donor. The resultant catalyst with the optimized Co/Re ratio of 1:1 can achieve an exceptional COL selectivity of 89% with a CAL conversion of 99% under mild conditions of 140 °C for 4 h, and the catalyst can be reused four times without loss of activity. Meanwhile, the Co₁Re₁/TiO₂/FA system was efficient for the selective hydrogenation of various α,β-unsaturated aldehydes to the corresponding α,β-unsaturated alcohols. The presence of ReO_x on the Co₁Re₁/TiO₂ catalyst surface was advantageous to the adsorption of C=O, and the ultrafine Co nanoparticles provided abundant hydrogenation active sites for the selective hydrogenation. Moreover, FA as a hydrogen donor improved the selectivity to α,β-unsaturated alcohols.

Highly stable Pt-Co bimetallic catalysts prepared by atomic layer deposition for selective hydrogenation of cinnamaldehyde

Pt-Co bimetallic catalysts were deposited onγ-Al₂O₃nanoparticles by atomic layer deposition (ALD) and were used for selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL). High resolution transmission electron microscopy, hydrogen temperature-programmed reduction, x-ray diffraction, and x-ray photoelectron spectroscopy were used to identify the strong interaction between Pt and Co. The obtained catalysts with an optimal Pt/Co ratio achieved a COL selectivity of 81.2% with a CAL conversion of 95.2% under mild conditions (i.e., 10 bar H₂and 80 °C). During the CAL hydrogenation, the addition of Co on Pt significantly improved the activity and selectivity due to the synergetic effects of Pt-Co bimetallic catalysts, resulted from the transfer of electrons from Co to Pt, which can stabilize the carbonyl groups. The obtained Pt-Co bimetallic catalysts also showed excellent stability due to the strong interaction between the metal nanoparticles and the alumina support. Negligible losses in the activity and selectivity were observed during the recycling experiments, showing the potential for practical applications.

Formation and selected catalytic properties of ruthenium, rhodium, osmium and iridium nanoparticles

The synthesis and applications in catalysis of nanoparticles formed from ruthenium, rhodium, osmium and iridium have been reviewed.

Copper(i) pyrimidine-2-thiolate cluster-based polymers as bifunctional visible-light-photocatalysts for chemoselective transfer hydrogenation of α,β-unsaturated carbonyls

The photoinduced chemoselective transfer hydrogenation of unsaturated carbonyls to allylic alcohols has been accomplished using cluster-based MOFs as bifunctional visible photocatalysts.

Fabrication of Ir-CoOx@mesoporous SiO2 Nanoreactors for Selective Hydrogenation of Substituted Nitroaromatics

Nanosized Ir catalysts suffer from serious side reactions and poor stability during hydrogenation of substituted nitroaromatics to produce aromatic amines. In this work, core-shell nanostructures with sub-4 nm Ir-CoO_x hybrid cores and mesoporous SiO₂ shells were designed and prepared to overcome these problems. The Ir-CoO_x hybrid cores were converted from IrCo alloy nanoparticles (NPs) inside SiO₂ through in situ calcination and reduction pretreatments. The SiO₂ mesoporous shells in Ir-CoO_x@SiO₂ nanoreactors prevented the agglomeration/sintering of IrCo NPs, while allowing the free reactants and products (big molecules). The synergy between Ir and CoO_x species improved H₂ adsorption, thus affecting the reaction rate as well as the selectivity to aromatic amines. As a result, the obtained Ir-CoO_x@SiO₂ nanocatalyst showed tremendous improvement in catalytic activity, selectivity, and stability.

Molybdenum-Incorporated Mesoporous Silica: Surface Engineering toward Enhanced Metal-Support Interactions and Efficient Hydrogenation

In heterogeneous catalysis, strong metal-support interactions are highly desired to improve catalytic turnover on metal catalysts. Herein, molybdenum is uniformly incorporated into mesoporous silica (KIT-6) to accomplish strong interactions with iridium catalysts, and consequently, active and selective hydrogenation of carbonyl compounds. Mo-incorporated KIT-6 (Mo-KIT-6) affords electronic interactions to improve the proportion of metallic Ir⁰ species, avoiding the easy surface oxidation of ultrafine metals in silica mesocavities. Owing to the effective H₂ activation and subsequent hydrogenation on metallic Ir⁰ sites, optimal Ir/Mo-KIT-6 with a high Ir⁰/Ir^δ+ ratio delivers prominent performance in the hydrogenation of amides to amines and α,β-unsaturated aldehydes to unsaturated alcohols. As for N-acetylmorpholine hydrogenation, the Ir/Mo-KIT-6 catalyst achieves efficient turnover toward N-ethylmorpholine with high selectivity (>99%) and exhibits activity that relies on the engineered chemical state of Ir sites. Such promotion is further proved to be universal in cinnamaldehyde hydrogenation. This work will provide new opportunities for catalyst design through surface/interface engineering.

Enhancing formaldehyde oxidation on iridium catalysts using hydrogenated TiO2 supports

Hydrogenated TiO₂ nanoparticles with rich hydroxyls were utilized as robust supports for Ir, accomplishing an obviously improved HCHO oxidation.