Preparation of Sn-modified silica-coated Pt catalysts: A new PtSn bimetallic model catalyst for selective hydrogenation of crotonaldehyde

Double solvent synthesis of ultrafine Pt nanoparticles supported on halloysite nanotubes for chemoselective cinnamaldehyde hydrogenation

The development of highly active, low cost and durable catalysts for selective hydrogenation of aldehydes is imperative and challenging. In this contribution, we rationally constructed ultrafine Pt nanoparticles (Pt NPs) supported on the internal and external surfaces of halloysite nanotubes (HNTs) by a facile double solvent strategy. The influence of Pt loading, HNTs surface properties, reaction temperature, reaction time, H₂ pressure and solvents on the performance of cinnamaldehyde (CMA) hydrogenation was analyzed. The optimal catalysts with the Pt loading of 3.8 wt% and the average Pt particle size of 2.98 nm exhibited outstanding catalytic activity for the hydrogenation of CMA to cinnamyl alcohol (CMO) with 94.1% conversion of CMA and 95.1% selectivity to CMO. More impressively, the catalyst showed excellent stability during six cycles of use. The ultra-small size and high dispersion of Pt NPs, the negative charge on the outer surface of HNTs, the -OH on the inner surface of HNTs, and the polarity of anhydrous ethanol solvent account for the outstanding catalytic performance. This work offers a promising way to develop high-efficiency catalysts with high CMO selectivity and stability by combining clay mineral halloysite and ultrafine nanoparticles.

Catalysis in Single Crystalline Materials: From Discrete Molecules to Metal-Organic Frameworks

Catalysis is one of the key techniques for people's modern life. It has created numerous essential chemicals such as biomedicines, agricultural chemicals and unique materials. Heterogeneous catalysis is the new emerging method with reusable catalysts. Among heterogenous catalysis patterns developed so far, single crystalline catalysis has become the promising one owing to its high catalytic density and selectivity resulted by the inherent porosity, orderliness of the lattices and permeability. These crystalline catalysts could be used in various reactions such as photo-dimerization, Diels-Alder reaction, CO₂ transformation and so on. In this review, we highlighted the reported works about the single crystalline catalysts. Both discrete small molecules and metal-organic frameworks (MOFs) have been used to prepare single crystals for catalysis. For discrete molecules based crystalline catalysts, coordinated and covalent molecules have been used. There were more catalytic modes in crystalline MOF catalysts. Three patterns were identified in this review: single crystalline MOFs i) without catalytic sites, ii) with inherent catalytic features and iii) with introducing catalytic units by post synthetic modification. Based on these examples, this review committed to provide the inspirations for the further design and application of single crystalline materials.

In situ tuning of electronic structure of catalysts using controllable hydrogen spillover for enhanced selectivity

In situ tuning of the electronic structure of active sites is a long-standing challenge. Herein, we propose a strategy by controlling the hydrogen spillover distance to in situ tune the electronic structure. The strategy is demonstrated to be feasible with the assistance of CoO_x/Al₂O₃/Pt catalysts prepared by atomic layer deposition in which CoO_x and Pt nanoparticles are separated by hollow Al₂O₃ nanotubes. The strength of hydrogen spillover from Pt to CoO_x can be precisely tailored by varying the Al₂O₃ thickness. Using CoO_x/Al₂O₃ catalyzed styrene epoxidation as an example, the CoO_x/Al₂O₃/Pt with 7 nm Al₂O₃ layer exhibits greatly enhanced selectivity (from 74.3% to 94.8%) when H₂ is added. The enhanced selectivity is attributed to the introduction of controllable hydrogen spillover, resulting in the reduction of CoO_x during the reaction. Our method is also effective for the epoxidation of styrene derivatives. We anticipate this method is a general strategy for other reactions.

In situ tuning of the electronic structure of active sites is a long-standing challenge. Here, the authors report an approach to tune the electronic structure of cobalt species during the styrene epoxidation reaction by the introduction of controllable hydrogen spillover for enhanced selectivity.

Effect of Hydrotalcites Interlayer Water on Pt-Catalyzed Aqueous-Phase Selective Hydrogenation of Cinnamaldehyde

The heterogeneous hydrogenation of α,β-unsaturated compounds requires understanding of the structure-activity relationship of metallic catalysts in consideration of solvent-mediated processes. In this work, a CoAl hydrotalcites (CoAl-HTs)-supported Pt nanoparticle catalyst is employed to study the effect of solvent water and HTs interlayer water on the aqueous-phase selective hydrogenation of cinnamaldehyde (CALD). Pt/Co₂Al₁-HTs catalyst displays 5075 h^-1 of specific reaction rate and 89% of C═O hydrogenation selectivity at 80 °C under 20 bar of H₂. Combined results of isotope-labeling experiments and theoretical DFT calculations demonstrate that the water-mediated hydrogen-exchange pathway exists in the reaction with a relatively lower-energy barrier in comparison to the direct H₂-dissociated hydrogenation pathway. The results also reveal that the interlayer water species of HTs support participate in the hydrogen-exchange reaction. Based on the H₂-D₂ exchange results, these HTs interlayer water species can promote H₂ activation and dissociation processes and thus accelerate the CALD hydrogenation reaction even under solvent-free conditions.

Selective hydrogenation of 2-pentenal using highly dispersed Pt catalysts supported on ZnSnAl mixed metal oxides derived from layered double hydroxides

Highly dispersed Pt catalysts supported on ZnSnAl mixed metal oxides showed high selectivity for 2-pentenol in selective hydrogenation of 2-pentenal.

Shining light on the solid–liquid interface: in situ/operando monitoring of surface catalysis

Many industrially important chemical transformations occur at the interface between a solid catalyst and liquid reactants. In situ and operando spectroscopies offer unique insight into the reactivity of such catalytically active solid–liquid interfaces.

Well-Defined Materials for Heterogeneous Catalysis: From Nanoparticles to Isolated Single-Atom Sites

The use of well-defined materials in heterogeneous catalysis will open up numerous new opportunities for the development of advanced catalysts to address the global challenges in energy and the environment. This review surveys the roles of nanoparticles and isolated single atom sites in catalytic reactions. In the second section, the effects of size, shape, and metal-support interactions are discussed for nanostructured catalysts. Case studies are summarized to illustrate the dynamics of structure evolution of well-defined nanoparticles under certain reaction conditions. In the third section, we review the syntheses and catalytic applications of isolated single atomic sites anchored on different types of supports. In the final part, we conclude by highlighting the challenges and opportunities of well-defined materials for catalyst development and gaining a fundamental understanding of their active sites.

Hydrogen Diffusion Guided Design of Pt-Based Alloys for Inhibition of Butadiene Over-Hydrogenation

Alloying Pt with other metals is an effective strategy to tune its performance towards selective hydrogenation reactions. Herein, we have demonstrated a process to screen Pt-based alloys for inhibition of butadiene over-hydrogenation with a model comprising isolated single atoms (ISA) embedded into Pt(111). DFT calculations reveal that the diffusion energy barrier of H co-adsorbed with 1-butene is a key parameter for the screening. The output from the ISA model was validated by testing several typical Pt-based alloys towards butadiene hydrogenation. Furthermore, an unexpected higher selectivity to cis-2-butene compared to the trans isomer and 1-butene over the PtZn alloy was explored employing the ISA model.

Insight into the structure evolution and the associated catalytic behavior of highly dispersed Pt and PtSn catalysts supported on La2O2CO3 nanorods

This work reports the composition-dependent structure evolution and the associated catalytic behavior of PtSn catalysts supported on La₂O₂CO₃ nanorods.

Electronic interactions between a stable electride and a nano-alloy control the chemoselective reduction reaction

The electronic effects induced by the synergy of stable C12A7:e^– electride and bimetallic Ru–Fe nanoparticles efficiently control the chemoselective reduction reaction.

Controlling the electronic structure of heterogeneous metal catalysts is considered an efficient method to optimize catalytic activity. Here, we introduce a new electronic effect induced by the synergy of a stable electride and bimetallic nanoparticles for a chemoselective reduction reaction. The electride [Ca₂₄Al₂₈O₆₄]⁴⁺·(e^–)₄, with extremely low work function, promotes the superior activity and selectivity of a Ru–Fe nano-alloy for the conversion of α,β-unsaturated aldehydes to unsaturated alcohols in a solvent-free system. The catalyst is easily separable from the product solution and reusable without notable deactivation. Mechanistic studies demonstrate that electron injection from the electride to the Ru–Fe bimetallic nanoparticles promotes H₂ dissociation on the highly charged active metal and preferential adsorption of C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O bonds over C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> Cs bond of the unsaturated aldehydes, to obtain the thermodynamically unfavorable but industrially important product.

Synergistic effect of Mo2N and Pt for promoted selective hydrogenation of cinnamaldehyde over Pt–Mo2N/SBA-15

Pt–Mo₂N/SBA-15 exhibits high activity for selective hydrogenation of cinnamaldehyde due to the synergistic effect between Mo₂N and Pt.

Pt@SnOx/SiO2 catalysts with enhanced selectivity to allyl alcohol for acrolein hydrogenation

A core–shell structure of Pt@SnO_x/SiO₂ catalyst was developed for the hydrogenation of acrolein with high activity and selectivity to allyl alcohol.

Highly selective hydrogenation of α,β-unsaturated aldehydes by Pt catalysts supported on Fe-based layered double hydroxides and derived mixed metal oxides

The selective hydrogenation of cinnamaldehyde and citral was investigated over platinum catalysts supported on Fe-based layered double hydroxides and derived mixed metal oxides.

SnO2-isolated Pt3Sn alloy on reduced graphene oxide: an efficient catalyst for selective hydrogenation of CO in unsaturated aldehydes

A pyramid shaped Pt₃Sn/SnO₂/rGO hybrid is highly active, selective and stable for the hydrogenation of the CO bond in unsaturated aldehydes to unsaturated alcohols under mild conditions.

A stepwise loading method to magnetically responsive Pt-Fe3O 4/MCNT catalysts for selective hydrogenation of 3-methylcrotonaldehyde

Pt-loaded multi-walled carbon nanotubes (Pt/MCNTs) and magnetically responsive Pt-Fe3O4/MCNT catalysts were prepared by a stepwise loading of preformed Pt and Fe3O4 nanoparticles onto multi-walled carbon nanotubes (MCNTs). The structure, composition, and magnetism of the catalysts were characterized by X-ray diffraction (XRD), TEM, H2-O2 titration, inductively coupling plasma-atomic emission spectroscopy (ICP-AES), and superconducting quantum interference device (SQUID) techniques. Ascribed to the well-controlled particle size in the preformed Pt colloids, Pt particles in the consequent Pt/MCNT and Pt-Fe3O4/MCNT catalysts are of high uniformity and dispersion. The prepared Pt catalysts show an excellent catalytic performance in the liquid phase hydrogenation of 3-methylcrotonaldehyde, one of typical α,β-unsaturated aldehydes. A very high selectivity to 3-methylcrotonalcohol of 98% at a conversion of about 80% was available on the magnetic Pt-Fe3O4/MCNT catalyst. The magnetic catalyst, with good superparamagnetism, can be easily recovered from the liquid phase system under the external magnetic field. Moreover, both the Pt/MCNT and magnetic Pt-Fe3O4/MCNT catalysts show a good recyclability, confirmed by five cycles of reusage.