Catalysts For Selective Hydrogenation Research Articles

Surface Engineering of Noble Metal Nanocrystals for Selective Hydrogenation

The selective hydrogenation has attracted increasing attention to chemists for the production of value‐added products in chemical industry. Over the past several decades, substantial effort has been devoted to the design of catalyst for the selective hydrogenation of light alkynes and α, β‐unsaturated aldehydes, two classic cases for selective hydrogenation in chemical industry. Despite the great progress, it remains great challenges to achieve the selective hydrogenation because the desired products are generally thermodynamically unfavored. Here, we summarize the recent advances on selective hydrogenation using noble metal nanocrystals, with an emphasis on the surface engineering of noble metal nanocrystals for the selective hydrogenation of light alkynes and α, β‐unsaturated aldehydes. We will highlight the strategies for surface engineering, the advanced techniques for characterizations, as well as mechanism studies. We hope this review will promote chemists to develop efficient and robust catalysts for selective hydrogenation.

Selective Hydrogenation of 2‐Methyl‐3‐butyn‐2‐ol Over Supported Cu Nanocatalysts

Nanosized copper is an interesting alternative to noble metal‐based catalysts in gas phase selective hydrogenation, but little is known about its performance in liquid phase catalysis. We investigated the activity and selectivity of 2 and 7 nm Cu on SiO2 catalysts for the three‐phase partial hydrogenation of 2‐methyl‐3‐butyn‐2‐ol, a highly relevant reaction for fine chemical synthesis. Next to the desired 2‐methyl‐3‐buten‐2‐ol, also 2‐methyl‐2‐butanol was formed as a result of over‐hydrogenation. The 7 nm Cu nanoparticles were intrinsically 2.5 times more active than 2 nm Cu (in terms of turnover frequency), and they were also more selective. At 180 °C the selectivity was only 15% at 50% conversion, but lowering the reaction temperature to 160 and 140°C led to 80% and even ~100% selectivity (at 50% conversion). The unselective step was around two times faster than the selective one, hence the high selectivity is due the stronger adsorption of the reactant than of the desired product, which limits over‐hydrogenation.

MOF-Derived ZrO2-Supported Bimetallic Pd-Ni Catalyst for Selective Hydrogenation of 1,3-Butadiene.

A series of MOF-derived ZrO2-supported Pd-Ni bimetallic catalysts (PdNi/UiO-67-CTAB(n)-A500) were prepared by co-impregnation and pyrolysis at 500 °C under air atmosphere using UiO-67-CTAB(n) (CTAB: cetyltrimethylammonium bromide; n: the concentration of CTAB; n = 0, 3, 8, 13, 18) as a sacrificial template. The catalytic activity of PdNi/UiO-66-CTAB(n)-A500 in 1,3-butadiene hydrogenation was found to be dependent on the crystal morphology of the UiO-67 template. The highest activity was observed over the PdNi/UiO-67-CTAB(3)-A500 catalyst which was synthesized using UiO-67-CTAB(3) with uniform octahedral morphology as the template for the 1,3-butadiene selective hydrogenation. The 1,3-butadiene conversion and total butene selectivity were 98.4% and 44.8% at 40 °C within 1 h for the PdNi/UiO-67-CTAB(3)-A500 catalyst, respectively. The catalyst of PdNi/UiO-67-CTAB(3)-A500 can be regenerated in flowing N2 at 200 °C. Carbon deposited on the surface of the catalyst was the main reason for its deactivation. This work is valuable for the high-efficiency bimetallic catalyst's development on the selective hydrogenation of 1,3-butadiene.

NaOH-assisted synthesis of N-doped carbon-encapsulated trimetallic CoNiZnO@NC catalyst for efficient selective hydrogenation of furfural to furfuryl alcohol

NaOH-assisted synthesis of N-doped carbon-encapsulated trimetallic CoNiZnO@NC catalyst for efficient selective hydrogenation of furfural to furfuryl alcohol

Chitosan as a Bio-Based Ligand for the Production of Hydrogenation Catalysts.

Bio-based polymers are attracting increasing interest as alternatives to harmful and environmentally concerning non-biodegradable fossil-based products. In particular, bio-based polymers may be employed as ligands for the preparation of metal nanoparticles (M(0)NPs). In this study, chitosan (CS) was used for the stabilization of Ru(0) and Rh(0) metal nanoparticles (MNPs), prepared by simply mixing RhCl3 × 3H2O or RuCl3 with an aqueous solution of CS, followed by NaBH4 reduction. The formation of M(0)NPs-CS was confirmed by Fourier Transform Infrared Spectroscopy (FT-IR), Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Analysis (EDX), Transmission Electron Microscopy (TEM) and X-ray Diffraction (XRD). Their size was estimated to be below 40 nm for Rh(0)-CS and 10nm for Ru(0)-CS by SEM analysis. M(0)NPs-CS were employed for the hydrogenation of (E)-cinnamic aldehyde and levulinic acid. Easy recovery by liquid-liquid extraction made it possible to separate the catalyst from the reaction products. Recycling experiments demonstrated that M(0)NPs-CS were highly efficient up to four times in the best hydrogenation conditions. The data found in this study show that CS is an excellent ligand for the stabilization of Rh(0) and Ru(0) nanoparticles, allowing the production of some of the most efficient, selective and recyclable hydrogenation catalysts known in the literature.

In situ exsolution to fabricate interfacial Ni0/Niδ+ sites for regulating reaction pathways in hydrogenation

Regulating the selectivity of reaction pathways to desirable products via controlling adsorption/activation behaviors towards reactants is significant for the design of excellent catalysts for selective hydrogenation but remains challenging. Exemplified with dimethyl oxalate (DMO) hydrogenation, we herein propose an in situ exsolution strategy for constructing interfacial Ni0/Niδ+ sites by using pre-synthesized Ni phyllosilicate as the precursor to control the reaction pathways of selective hydrogenation. Structural characterizations, including in situ spectroscopic and isotopic studies, and theoretical calculations elucidate that the interfacial Ni0/Niδ+ sites can selectively activate monoester group of DMO via a tilted adsorption configuration and hence boost hydrogen dissociation. With such activation behaviors the reaction pathway is steered to methyl glycolate, other than the pathway to ethylene glycol on the reference active sites where both ester groups are activated and methyl formate is formed via breaking the C–C bond of DMO.

Scaling-Up Microwave-Assisted Synthesis of Highly Defective Pd@UiO-66-NH2 Catalysts for Selective Olefin Hydrogenation under Ambient Conditions.

The need to develop green and cost-effective industrial catalytic processes has led to growing interest in preparing more robust, efficient, and selective heterogeneous catalysts at a large scale. In this regard, microwave-assisted synthesis is a fast method for fabricating heterogeneous catalysts (including metal oxides, zeolites, metal-organic frameworks, and supported metal nanoparticles) with enhanced catalytic properties, enabling synthesis scale-up. Herein, the synthesis of nanosized UiO-66-NH2 was optimized via a microwave-assisted hydrothermal method to obtain defective matrices essential for the stabilization of metal nanoparticles, promoting catalytically active sites for hydrogenation reactions (760 kg·m-3·day-1 space time yield, STY). Then, this protocol was scaled up in a multimodal microwave reactor, reaching 86% yield (ca. 1 g, 1450 kg·m-3·day-1 STY) in only 30 min. Afterward, Pd nanoparticles were formed in situ decorating the nanoMOF by an effective and fast microwave-assisted hydrothermal method, resulting in the formation of Pd@UiO-66-NH2 composites. Both the localization and oxidation states of Pd nanoparticles (NPs) in the MOF were achieved using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), respectively. The optimal composite, loaded with 1.7 wt % Pd, exhibited an extraordinary catalytic activity (>95% yield, 100% selectivity) under mild conditions (1 bar H2, 25 °C, 1 h reaction time), not only in the selective hydrogenation of a variety of single alkenes (1-hexene, 1-octene, 1-tridecene, cyclohexene, and tetraphenyl ethylene) but also in the conversion of a complex mixture of alkenes (i.e., 1-hexene, 1-tridecene, and anethole). The results showed a powerful interaction and synergy between the active phase (Pd NPs) and the catalytic porous scaffold (UiO-66-NH2), which are essential for the selectivity and recyclability.

Supported ruthenium phosphide as a promising catalyst for selective hydrogenation of sugars

This work demonstrates that ruthenium phosphides (RuP2) are attractive catalysts for selective production of alditols by sugar hydrogenation. In our studies, carbon supported RuP2 with a ruthenium content of 5 wt.‐% led to the highest activity in xylose hydrogenation and to nearly 100 % yield for xylitol. ICP‐OES and XRD measurements revealed the stability of this novel RuP2/C catalyst under typical hydrogenation conditions (50 barH2, 120 °C) in aqueous phase. Furthermore, STEM‐EDX illustrated the close proximity of ruthenium and phosphorous on the catalyst site and the formation of nanoparticles in the size of 2‐4 nm. The novel catalyst system was successfully applied for the selective hydrogenation of further sugar substrates, including glucose, fructose, and disaccharides, such as cellobiose and sucrose. Here, the RuP2/C revealed its bifunctional acidic/metallic character, enabling in a tandem reaction the hydrolysis of disaccharides, directly followed by a selective hydrogenation to form sugar alcohols in high yield.

Pt–Fe–Al Trimetallic Nanoporous Catalyst for Selective Hydrogenation of α,β-Unsaturated Aldehydes

Pt–Fe–Al Trimetallic Nanoporous Catalyst for Selective Hydrogenation of α,β-Unsaturated Aldehydes

Cyclometallated Imides as Templates for the H-Bond Directed Iridium-Catalyzed Asymmetric Hydrogenation of N-Methyl, N-Alkyl and N-Aryl Imines.

A combined computational and experimental approach allowed us to develop the most selective catalysts for the direct hydrogenation of N-methyl and N-alkyl imines described to date. Iridium catalysts with a cyclometallated cyclic imide group provide selectivity of up to 99% enantiomeric excess. Computational studies show that the selectivity results from the combined effect of H-bonding of the imide C=O with the substrate iminium ion and a stabilizing π-π interaction with the cyclometallated ligand. The cyclometallated ligand thus exhibits a unique mode of action, serving as a template for the H-bond directed approach of the substrate which results in enhanced selectivity. The catalyst (2) has been synthesized and isolated as a crystalline air-stable solid. X-ray analysis of 2 confirmed the structure of the catalyst and the correct position of the imide C=O groups to engage in an H-bond with the substrate. 19F-NMR real-time monitoring showed the hydrogenation of N-methyl imines catalyzed by 2 is very fast, with a TOF of approx. 3500 h-1.

Deprotonated 2-thiolimidazole serves as a metal-free electrocatalyst for selective acetylene hydrogenation.

Metal-free catalysts offer a desirable alternative to traditional metal-based electrocatalysts. However, metal-free catalysts, featuring defined active sites, rarely show activities as promising as metal-based materials. Here we report 2-thiolimidazole as an efficient metal-free catalyst for selective electrocatalytic hydrogenation of acetylene into ethylene. Under alkaline conditions, the sulfhydryl and imino groups of 2-thiolimidazole are spontaneously deprotonated into dianions. Deprotonation thus enriches the negative charges of pyridinic N sites in 2-thiolimidazole to enhance the adsorption of electrophilic acetylene through the σ-configuration. Ethylene partial current densities show a volcano relationship with the negative charges of the pyridinic N sites in various imidazole derivatives. Consequently, the deprotonated 2-thiolimidazole exhibits an ethylene partial current density and faradaic efficiency competitive with metal-based catalysts like Cu and Pd. This work highlights the tunability and promising potential of metal-free molecules in electrocatalysis.

Development of Fe-based catalysts for CO2 hydrogenation to higher hydrocarbons for operating in slurry reactor

The development of CO2 hydrogenation catalysts for hydrocarbon production is a challenging and relevant task as it can contribute to solving of the CO2 emission problem. In the present work, we describe our journey in the development of catalysts for operating in a slurry reactor. The screening of the preparation methods and catalyst composition yielded an active and highly selective CO2 hydrogenation catalyst with catalytic performances comparable to the best ones reported in the literature. The most perspective catalysts were successfully evaluated in CO2 hydrogenation using a slurry reactor. The supported catalysts were found to have a lower ability to form higher hydrocarbons compared to bulk catalysts. This could be correlated with the particle sizes of the active component of the respective catalysts. This insight may be useful in preparing tailor-made Fe-based catalysts with high chain growth probability. The important issue of mechanical strength for slurry operation was highlighted.

Investigating the Long-Term Kinetics of Pd Nanoparticles Prepared from Microemulsions and the Lindlar Catalyst for Selective Hydrogenation of 3-Hexyn-1-ol

Investigating the Long-Term Kinetics of Pd Nanoparticles Prepared from Microemulsions and the Lindlar Catalyst for Selective Hydrogenation of 3-Hexyn-1-ol

Promotional effects of Nb2O5 on ceria doped Ni catalysts for selective hydrogenation of 1,3-butadiene to butenes: Combined experimental and DFT approach

Developing low cost, active and selective catalysts that would replace the more deployed noble metals is desirable for hydrogenation of 1,3-butadiene. Herein, we prepared Ni catalysts supported on niobium-cerium oxides and characterization was carried out with TGA, XRD, H2-TPR, H2-TPD, HR-TEM, XPS, FTIR, N2 adsorption–desorption, and EDS mapping. Density functional theory (DFT) computes the reaction energies controlling the 1,3-butadiene hydrogenation. H2-TPR revealed that the inclusion of niobium oxide in the catalysts confer stronger metal support interaction that promotes the surface and bulk reduction of cerium oxide and leads to the improvement in the formation of surface Ce3+ as confirmed from the XPS analysis. 1,3-butadiene conversion was tested between 100 °C-350 °C and the catalysts exhibit high conversion at lower Ni loading. We found that the niobium inclusion directed the selectivity towards near complete butene formation even at higher temperature. The onset of decline in activity was observed at temperatures above 250 °C with the simultaneous formation of propene and propane and the disappearance of butane. Guided by the reaction results and the temperature programmed oxidation analysis (TPO), we proposed the reaction mechanism leading to the deactivation, and this entails butane decomposition to propene and surface carbene, while propane is formed from propene, the surface carbene occasioned in the formation of harmful carbon as evident from TPO results. Carbonaceous species formed on the catalysts were minimized on the niobium containing catalysts.

Cu@SiO2 catalyst with high copper dispersion for chemoselective hydrogenation of p-chloronitrobenzene

Selective hydrogenation of p-chloronitrobenzene (p-CNB) is not only of significant industrial importance, but also an important model reaction for selectivity investigation. Despite non-precious metal Cu has been proven to be an effective promoter in bimetallic catalysts, Cu as a single active metal achieving both high conversion and high selectivity are rare reported. In this work, Cu@SiO2 catalysts with high specific surface area (509.8–694.3 m2/g), high Cu dispersion (58.4–69.6 %), and small particle size (2.0–3.0 nm) has been prepared by a simple sol–gel method. The catalysts completely suppress the dechlorination reaction, achieving complete conversion of p-CNB with 99.9 % selectivity for p-chloroaniline (p-CAN). Its microstructure, composition, chemical state, adsorption and reaction behavior have been identified by various conventional ex-situ characterizations of catalysts and in-situ DRIFTs of hydrogenation of p-CNB. Interestingly, even at high loadings, Cu in the catalyst could be highly dispersed, thus exhibiting good catalytic activity. In addition, the Cu catalyst exhibits unique adsorption performance towards p-CNB, which perhaps one of the factors for its good performance. This work not only provides a selective hydrogenation catalyst with high Cu dispersion even at high loading amount by a simple method and but also reveals the importance of the adsorption mode of p-CNB, providing guidance for the development of more efficient catalysts in the future.

SSZ-39 zeolite-based Ru catalysts for selective hydrogenation of levulinic acid to γ-valerolactone: Influence of synthesis method and zeolite acidity

Novel SSZ-39 zeolite-based Ru catalysts were synthesized by impregnation on as-synthesized metallic and protonated SSZ-39 and a one-pot synthesis strategy. The study focused on the influence of the SSZ-39 zeolite characteristics and catalyst preparation method type toward levulinic acid (LA) selective conversion to γ-valerolactone (GVL) under relatively mild reaction conditions (150 °C, 4 h and 2 MPa of H2 with H2O and THF as solvents). Catalysts exhibited excellent catalytic efficiency (100 % LA conversion and 98.3 % GVL selectivity) and remarkable hydrothermal stability. The results revealed a correlation between excellent catalytic activity and the structural features of the synthesized catalysts, predominantly dependent on their appropriate surface acidity (strong Lewis acid sites) and enhanced electronic interaction between Ru species and SSZ-39. The one-pot method promoted the formation of mesopores besides the zeolitic micropores present in SSZ-39; therefore, the catalyst prepared by the one-pot method (Ru/SSZ-39) showed purer SSZ-39 crystallites and a slightly larger catalytic surface area of 439 m2/g than the original zeolite surface area of 424 m2/g. In addition, the original zeolite crystals retained their morphology as spherical aggregates and remained unaffected by Ru impregnation on the metallic or protonated support during the synthesis of Ru/Na-SSZ-39 and Ru/H-SSZ-39 catalysts, respectively. Notably, it has been demonstrated that SSZ-39 zeolite effectively acts as a support for the preparation of Ru catalyst in biomass conversion reactions. Moreover, the reused catalyst exhibited consistent activity over six cycles, maintaining its structural framework without significant loss in activity.

Hydrogenation of olefinic bonds in nitrile butadiene rubber on single-atom Pd1/CeO2−x catalysts with ultrahigh mass activity and stability

As pivotal high-performance elastomers, hydrogenated nitrile butadiene rubber (HNBR) was commonly manufactured by selective hydrogenation of nitrile butadiene rubber (NBR). Nevertheless, the high cost and poor stability of current noble metal-based catalysts seriously limit their large-scale applications. Herein, we report single-atom Pd supported by oxygen vacancies-rich CeO2−x nanorods (Pd1/CeO2−x) as a novel catalyst for selectively hydrogenating the NBR. As a result of strong interaction between single-atom Pd and CeO2−x support, the electrophilicity of Pd sites, and the nucleophilicity of olefinic bonds in NBR, the Pd1/CeO2−x show a very high hydrogenated degree of 97.6 %, an unprecedentedly high Pd mass activity of 93.9 gNBR gPd−1h−1, and outstanding cycling stability, which considerably outperform those for previously reported catalysts. Therefore, this work will promote the low-cost manufacture of HNBR and the exploration of single-atom catalysts for selective hydrogenation.

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

Zinc-included intermetallic compound catalysts of RhZn, PtZn, and PdZn with a molar ration of Zn/metal = 1/1, which are generally prepared using a hydrogen reduction approach, are known to show excellent catalytic performance in some selective hydrogenations of organic compounds. In this study, in order to reduce the incorporated mounts of the expensive noble metals, we attempted to prepare zinc-rich intermetallic compounds via a CaH2-assisted molten salt synthesis method with a stronger reduction capacity than the common hydrogen reduction method. X-ray diffraction results indicated the formation of RhZn13 and Pt3Zn10 in the samples prepared by the reduction of ZnO-supported metal precursors. In a hydrogenation reaction of p-nitrophenol to p-aminophenol, the ZnO-supported RhZn13 and Pt3Zn10 catalysts showed a higher selectivity than the RhZn/ZnO and PtZn/ZnO catalysts with the almost similar conversions. Thus, it was demonstrated that the zinc-rich intermetallic compounds of RhZn13 and Pt3Zn10 could be superior selective hydrogenation catalysts compared to the conventional intermetallic compound catalysts of RhZn and PtZn.

Copper nanoparticles encapsulated in zeolitic imidazolate framework-8 as a stable and selective CO2 hydrogenation catalyst

Metal–organic frameworks have drawn attention as potential catalysts owing to their unique tunable surface chemistry and accessibility. However, their application in thermal catalysis has been limited because of their instability under harsh temperatures and pressures, such as the hydrogenation of CO2 to methanol. Herein, we use a controlled two-step method to synthesize finely dispersed Cu on a zeolitic imidazolate framework-8 (ZIF-8). This catalyst suffers a series of transformations during the CO2 hydrogenation to methanol, leading to ~14 nm Cu nanoparticles encapsulated on the Zn-based MOF that are highly active (2-fold higher methanol productivity than the commercial Cu–Zn–Al catalyst), very selective (>90%), and remarkably stable for over 150 h. In situ spectroscopy, density functional theory calculations, and kinetic results reveal the preferential adsorption sites, the preferential reaction pathways, and the reverse water gas shift reaction suppression over this catalyst. The developed material is robust, easy to synthesize, and active for CO2 utilization.

Design of efficient supported Pd-Co catalysts for selective hydrogenation of acetylene

The research is devoted to the study of active component formation in the novel Pd-Co catalysts supported on carbon material Sibunit. It was shown that 0.5 %Pd–0.5 %Co/C samples exhibit high ethylene yield in the acetylene hydrogenation process due to the presence of fcc PdxCo(1-x) particles. According to in situ XRD-TPR analysis, solid solution formation begins during the reduction of samples in H2 at T ≥ 500 °C. Using the EXAFS, XRD and EDX it was established that H2-treatment at 500 °C leads to the formation of ∼Pd0.6Co0.4 particles and an increase in the reduction temperature to 600 and 700 °C is accompanied by the enrichment of the Pd-Co-phase with cobalt to ∼Pd0.5Co0.5 and ∼Pd0.45Co0.55 compositions, respectively. The ethylene yield on Pd-Co/C catalysts reduced at 500, 600 and 700 °C is 56, 66 and 68 %, respectively, which significantly exceeds the ethylene quantity obtained on monometallic Pd/C samples (∼52 %). It is assumed that the excellent selectivity of Pd-Co/C samples treated in H2 at 600 and 700 °C is due to an increase in the amount of palladium atoms surrounded by cobalt and a change in the palladium electronic state (XPS).