Catalysts For Selective Hydrogenation Research Articles

Cyclic extrusion synthesis of mesoporous carbon‐supported metal catalysts for selective hydrogenation

AbstractThe mesoporous carbon‐supported metal catalysts are important materials in heterogeneous catalysis. From the standpoint of process intensification, the current synthesis methods still suffer from several issues, such as the excessive use of toxic solvents, the time‐consuming self‐assembly process, and the difficulty of continuous production. Herein, we report a solvent‐free and continuous route to synthesize mesoporous carbon‐supported metal catalysts. Interestingly, the use of cyclic extrusion could promote mixing, coordination, and assembly of catalyst precursors (tannin‐metal salts‐additives) by shearing and squeeze force. The as‐made mesoporous carbon‐supported nickel materials showed high surface areas (up to 512 m2 g−1), narrow pore size distribution (~10 nm), and good performance in the selective hydrogenation of nitrobenzene to aniline (Conv. >99%; Sel. >99%). In addition, the fluid property of catalyst precursors and the geometry of the twin‐screw extrusion channel were studied, and the essence of this cyclic extrusion process is also discussed.

Activated carbon supported nickel catalyst for selective CO2 hydrogenation to synthetic methane under contactless induction heating

The use of CO2 methanation in the power-to-gas (PtG) technology chains has received increasing attention in recent years for clean energy and sustainable development. In this work, macroscopic mesoporous nickel catalyst was prepared and evaluated for selective CO2 hydrogenation to CH4 using commercial activated carbon (AC) pellets. Catalyst samples were fully characterized by liquid N2 adsorption-desorption, X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), scanning and transmission electron microscopy (SEM/TEM). Catalytic performances were investigated under various reaction conditions with both direct induction heating (IH) and conventional indirect Joule heating (JH) modes. Results indicated that by simple thermal treatment, the surface and textural properties of the macroscopic carbon support could be greatly modified by improving the dispersion of metal sites and thus the catalytic performance. The advantages of IH combined with the inherent high thermal and electrical conductivity of the prepared materials could effectively avoid the temperature runaway and enhance the CO2 activation at relatively low reaction temperature. By comparison to the classical indirect JH mode, the resulting macroscopic nickel catalysts showed improving catalytic performances for CO2 methanation under IH mode. The efficient heat management under direct IH mode also prevented coke formation on the catalyst surface which contributes to its high stability as a function of time-on-stream.

Design of Flame‐Made ZnZrOx Catalysts for Sustainable Methanol Synthesis from CO2

AbstractMixed zinc‐zirconium oxides, ZnZrOx, are highly selective and stable catalysts for CO2 hydrogenation to methanol, a pivotal energy vector. However, their activity remains moderate, and descriptors to design improved systems are lacking. This work applies flame spray pyrolysis (FSP), a one‐step and scalable method, to synthesize a series of ZnZrOx catalysts, and systematically compares them to coprecipitated (CP) analogs to establish deeper synthesis–structure–performance relationships. FSP systems (up to 5 mol%) generally display a threefold higher methanol productivity compared to their CP counterparts. In‐depth characterization and theoretical simulations show that, unlike CP, FSP maximizes the surface area and formation of atomically dispersed Zn2+ sites incorporated in lattice positions within the ZrO2 surface, which is key to improving performance. Analysis by in situ electron paramagnetic resonance (EPR) spectroscopy reveals that the specific architecture of the flame‐made catalyst markedly fosters the generation of oxygen vacancies. Together with surrounding Zn and Zr‐O atoms, the oxygen vacancies create active ensembles that favor methanol formation through the formate path while suppressing undesired CO production, as confirmed by kinetic modeling. This study elucidates the nature of active sites and their working mechanism, pushing forward ZnZrOx‐catalyzed methanol synthesis by providing a new benchmark for this cost‐effective and earth‐abundant catalyst family.

Synthesis of Alumina Supported Pt-SnO2 Hybrid Nanostructures by In Situ Transformation of PtSn Alloy Nanoparticles and Their Application as Highly Efficient Catalysts for Selective Hydrogenation of Furfural

In this work, PtSn alloy nanoparticles were synthesized by coreduction of Pt and Sn precursors by ethylene glycol in the presence of stabilizing agents and then were in situ transformed into Pt-SnO2 hybrid nanostructures on alumina supports by calcination. Relative to Pt/Al2O3, Pt1-(SnO2)0.3/Al2O3 demonstrates improved catalytic efficiency for furfuryl alcohol production by furfural hydrogenation. Under the H2 pressure of 1.0 MPa, 100 °C, 3.0 h, and furfural/Pt molar ratio of 1435/1, the furfuryl alcohol yields could approach 98.2%. The enhancement of catalytic performance of the Pt-SnO2/Al2O3 could be ascribed to the formation of the close contact Pt-SnO2 interfaces, which is highly active for furfural hydrogenation due to the synergistic effect between Pt and SnO2.

Enhanced Alkene Selectivity for Transfer Semihydrogenation of Alkynes over Electron-Deficient Pt Nanoparticles Encapsulated in Hollow Silica Nanospheres.

In this work, we report that Pt nanoparticles confined in hollow porous silica nanospheres (Pt@HPSNs) function as highly selective catalysts for the transfer hydrogenation of phenylacetylene to styrene with ammonia borane. Relative to the deep hydrogenation of phenylacetylene to ethylbenzene over the supported Pt/SiO2, Pt@HPSNs exhibit above 88% of styrene selectivity at nearly 100% of phenylacetylene conversions, and the high selectivity of Pt@HPSNs can be maintained even at high ammonia borane/phenylacetylene ratios and longer reaction time. The Pt 4f X-ray photoelectron spectrum of Pt@HPSNs shows a remarkable ∼1.5 eV shift to high binding energy, proving the nature of electron deficiency of such encapsulated Pt nanoparticles. Combined with extremely minor transfer hydrogenation of styrene to ethylbenzene when styrene as substrates, the enhanced styrene selectivity of Pt@HPSNs is ascribed to the electron deficiency of encapsulated Pt nanoparticles, which leads to the fast desorption of styrene and thus avoids deep hydrogenation.

Enhanced Activity of Alkali-Treated ZSM-5 Zeolite-Supported Pt-Co Catalyst for Selective Hydrogenation of Cinnamaldehyde

A bimetallic Pt8Co1 supported on alkali-treated ZSM-5 zeolite (ZSM-5-AT) was prepared through the impregnation method. The structure and surface properties of the catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2-sorption and X-ray photoelectron spectroscopy (XPS) as well as temperature-programmed desorption of NH3 (NH3-TPD) and temperature-programmed reduction of H2 (H2-TPR). The TEM images present that the bimetallic Pt8Co1 nanoparticles with a mean particle size of 4-6 nm were uniformly dispersed on the alkali-treated ZSM-5 zeolite. The bimetallic Pt8Co1/ZSM-5-AT catalyst exhibited an extraordinary COL selectivity of 65% at a >99% CAL conversion efficiency, which showed a much higher catalytic performance (including the activity and selectivity) than the monometallic Pt/ZSM-5-AT and Co/ZSM-5-AT catalysts in the selective hydrogenation of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) using hydrogen as reducing agent. The high catalytic activity of the bimetallic catalyst was attributed to the higher electron density of Pt species and more acidic sites of the alkali-treated ZSM-5 zeolite support. The recovery test showed no obvious loss of its initial activity of the Pt8Co1/ZSM-5-AT catalyst for five times.

Towards stable nickel catalysts for selective hydrogenation of biomass-based BHMF into THFDM

Selective transformation of BHMF (2,5-bis(hydroxymethyl)furan) to THFDM (tetrahydrofuran-2,5-dimethanol) over a variety of structured Ni/Sx-Z1−x catalysts was investigated. The effects of support, Ni loading, solvent, temperature, pressure, and particle size on the conversion and selectivity were studied. Among them, the 10 wt% Ni catalyst supported on the SiO2:ZrO2 weight ratio of 90:10 (10NiS90Z10) exhibits the best performance in terms of BHMF conversion and THFDM selectivity. Its good performance was attributed to its well-balanced properties, that depend upon the ZrO2 content of the support in combination with SiO2, the active Ni sites-support interaction, and acidity/basicity ratio of each catalyst resulting in different Ni dispersions. Importantly, the 10NiS90Z10 catalyst showed a stable selectivity to THFDM (>94%), with 99.4% conversion of BHMF during 2 h reaction time. Poor catalytic activity resulted from excessive ZrO2 content (>10 wt%). The structural, textural, and acidity properties of NiSi100−y-Zry catalysts, tuned by selectively varying the Ni amount from 5 to 15 wt%, were critically investigated using numerous material characterization techniques. Catalyst recycling experiments revealed that the catalyst could be recycled several times without any measurable loss of catalytic activity.

Stable and Ordered Body-Centered Cubic PdCu Phase for Highly Selective Hydrogenation.

Phase engineering of nanomaterials plays a crucial role for regulating the catalytic performance. Nevertheless, great challenges still remain for elucidating the structure-selectivity correlation. Herein, this study demonstrates that the body-centered cubic phase of PdCu (bcc-PdCu) can serve as a highly active and selective catalyst for 3-nitrostyrene (NS) hydrogenation under mild conditions. In particular, bcc-PdCu displays a 3-nitro-ethylbenzene (NE) selectivity of 93.8% with a turnover frequency (TOF) value of 4573 h-1 at 30°C in the presence of H2 . With the assistance of NH3 ∙BH3 , the selectivity of 3-amino-styrene (AS) reaches 94.5% with a TOF value of 13719h-1 . Detailed experimental and theoretical calculations reveal that improved NE selectivity is ascribed to the selective adsorption of the CC bond and desorption of NE on bcc-PdCu. Moreover, the presence of NH3 ∙BH3 facilitates the selective hydrogenation of NO2 due to their strong interaction and thus leads to the formation of AS. This work provides an efficient selective catalyst for NS hydrogenation under mild conditions, which may attract immediate interests in the fields of materials, chemistry, and catalysis.

Selective semi-hydrogenation of alkynes on palladium-selenium nanocrystals

The selective hydrogenation of alkyne plays a crucial role in chemical industry, yet great challenges still remain for suppressing the over-hydrogenation to alkane while maintaining high activity. Herein, we demonstrate that palladium–selenium intermetallic nanocrystals (Pd4.5Se NCs, Pd4Se NCs, Pd7Se2 NCs, and Pd7Se4 NCs) can enable the semi-hydrogenation of alkyne to alkene. In situ characterizations and theoretical simulations indicate that the geometric and electronic synergetic effects of Pd–Se NCs can facilitate the σ-π associative adsorption of CC bond in alkyne but suppress the over-hydrogenation of alkene. In particular, Pd4.5Se NCs exhibit high selectivity to the semi-hydrogenation of phenylacetylene (PA) to styrene (≥98.0 %) in the full conversion range, which has outperformed Pd NCs/C and commercial Lindlar catalyst. This work expands the mechanism understanding of Pd-based catalysts for selective hydrogenation, which may attract great interests of researchers in material science, chemistry, and catalysis.

Boosting Chemoselective Hydrogenation of Nitroaromatic via Synergy of Hydrogen Spillover and Preferential Adsorption on Magnetically Recoverable Pt@Fe2 O3.

It is highly desired but challenging to design high performance catalyst for selective hydrogenation of nitro compounds into amino compounds. Herein, a boosting chemoselective hydrogenation strategy on Pt@Fe2 O3 is proposed with gradient oxygen vacancy by synergy of hydrogen spillover and preferential adsorption. Experimental and theoretical investigations reveal that the nitro is preferentially adsorbed onto oxygen vacancy of Pt@Fe2 O3 , meanwhile, the H2 dissociated on Pt nanoparticles and then spillover to approach the nitro for selective hydrogenation (>99% conversion of 4-nitrostyrene, > 99% selectivity of 4-aminostyrene, TOF of 2351h-1 ). Moreover, the iron oxide support endows the catalyst magnetic retrievability. This high activity, selectivity, and easy recovery strategy provide a promising avenue for selective hydrogenation catalysis of various nitroaromatic.

Atom-precise silver–palladium bimetallic clusters on carbon supports as selective hydrogenation catalysts

Ag24Pd1(SR)18 clusters are more active than their Ag25 counterparts, and they are highly selective hydrogenation catalysts for alkynol substrates.

M supported on Al-defective Al2-δO3 (M = Fe, Co, Ni, Cu, Ag, Au) as catalysts for acetylene semi-hydrogenation: a theoretical perspective.

Semi-hydrogenation of acetylene is of great importance for both industry and academia. High prices and limited supplements of noble metals leave room for developing base metal catalysts. Experiments revealed the atomically dispersed Cu supported by Al2O3 with excellent long-term stability and high ethylene selectivity, but the physical nature has rarely been investigated theoretically. DFT calculations and microkinetic modeling revealed that the surface OH species could stabilize Cu1/Al2-δO3 and enhance its catalytic performance. The selectivity of ethylene formation decreases with increasing copper clusters (e.g., Cu1/Al2-δO3> Cu4/Al2-δO3> Cu8/Al2-δO3), meaning that the atomically dispersed copper may be a potential candidate for acetylene semi-hydrogenation. The structures of a series of single site catalysts M1/Al2-δO3 (M = Fe, Co, Ni, Ag, Au) are similar to that of Cu1/Al2-δO3, but their performances in catalyzing acetylene semi-hydrogenation are different. M1/Al2-δO3 (M = Ag, Au) shows higher selectivity than Cu1/Al2-δO3, while M1/Al2-δO3 (M = Fe, Co, Ni) demonstrates a higher turnover frequency (TOF) of ethylene than Cu1/Al2-δO3. Moreover, our results indicate that the Ni1-Cu1/Al2-δO3 alloy shows both high activity and ethylene selectivity. The present results show a compensation between the reactivity and the selectivity, suggesting that alloys of VIIIB metals with IB metals like Ni1-Cu1/Al2-δO3 may be efficient candidate catalysts in acetylene selective hydrogenation.

Co–Cu–La catalysts for selective CO2 hydrogenation to higher hydrocarbons

Copper and lanthanum promoted cobalt catalysts for CO2 hydrogenation to higher hydrocarbons are described. The catalysts were prepared by the self-propagating high-temperature synthesis followed by alkaline leaching. They are active in CO2 hydrogenation at 200 °C under 10 bar pressure (CO2 : H2 = 1 : 3) with selectivity to C2+ alkanes up to 39%; no alkenes and alcohols are formed under these experimental conditions.

Utilization of γ-radiation in the synthesis of bimetallic Cu–Ni catalysts for selective vapour phase hydrogenation of levulinic acid to γ-valerolactone

A set of mono and bimetallic Cu–Ni systems supported on γ-alumina catalysts were synthesized using γ-radiation instead of conventional calcination and reduction.

Etching suppression as a means to Pt dendritic ultrathin nanosheets by seeded growth.

2D ultrathin metal nanostructures are emerging materials displaying distinct physical and chemical properties compared to their analogues of different dimensionalities. Nanosheets of fcc metals are intriguing, as their crystal structure does not favour a 2D configuration. Thanks to their increased surface-to-volume ratios and the optimal exposure of low-coordinated sites, 2D metal nanostructures can be advantageously exploited in catalysis. Synthesis approaches to ultrathin nanosheets of pure platinum are scarce compared to other noble metals and to Pt-based alloys. Here, we present the selective synthesis of Pt ultrathin nansosheets by a simple seeded-growth method. The most crucial point in our approach is the selective synthesis of Pt seeds comprising planar defects, a main driving force for the 2D growth of metals with fcc structure. Defect engineering is employed here, not in order to disintegrate, but for conserving the defect comprising seeds. This is achieved by in situ elimination of the principal etching agent, chloride, which is present in the PtCl2 precursor. As a result of etching suppression, twinned nuclei, that are selectively formed during the early stage of nucleation, survive and grow to multipods comprising planar defects. Using the twinned multipods as seeds for the subsequent 2D overgrowth of Pt from Pt(acac)2 yields ultrathin dendritic nanosheets, in which the planar defects are conserved. Using phenylacetylene hydrogenation as a model reaction of selective hydrogenation, we compared the performance of Pt nanosheets to that of a commercial Pt/C catalyst. The Pt nanosheets show better stability and much higher selectivity to styrene than the commercial Pt/C catalyst for comparable activity.

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.

Engineering an egg-shell structure for the Ag/SiO2 pellet catalyst for selective hydrogenation of dimethyl oxalate to methyl glycolate

An egg-shell-type Ag/SiO2 pellet catalyst with an optimized thickness of the Ag-shell exhibits both enhanced activity and selectivity for DMO hydrogenation to MG.

Insights into structure–activity relationships in efficient silica-supported Ni catalysts for selective hydrogenation of levulinic acid

Upgrading biomass-derived levulinic acid (LA) with greater carbonyl (CO) group activation is crucial in converting biomass and its derivatives into valuable biochemicals and biofuels.

Recent research advances on catalysts for selective hydrogenation of ethyne

In this review, recent advances in catalyst design for selective ethyne hydrogenation to ethylene are summarized, encouraging more in-depth research.

A novel and green synthesis of methylcyclohexane diisocyanate: Reaction properties, deactivation and regeneration of Rh/γ-Al2O3 catalyst in benzene ring selective hydrogenation

Methylcyclohexane diisocyanate (HTDI) is the core raw material for the synthesis of high-grade polyurethane. Aiming at the problems existing environmental pollution and safety risks in the phosgene process, a novel and green synthesis route of HTDI was proposed. We studied the catalytic hydrogenation of dimethyl toluene dicarbamate (TDC) benzene ring to methyl cyclohexyldicarbamate (HTDC) in this novel route. The effects of metal active components, supports and metal Rh loadings on the catalytic performance were investigated. It was found that the supported Rh/γ-Al2O3 catalyst had excellent catalytic activity and selectivity. The yield of HTDC was close to 100 % at 100 °C under 3 MPa hydrogen pressure. However, the catalyst was deactivated seriously after the reaction. The organic matter adsorbed on the catalyst surface and covered the active metal was the main reason for the catalyst deactivation. Fortunately, the deactivated catalyst could be regenerated by solvent washing and high temperature calcination.