Active Hydrogenation Catalysts Research Articles

Nano-sized Metallic Nickel Clusters Stabilized on Dealuminated beta-Zeolite: A Highly Active and Stable Ethylene Hydrogenation Catalyst

Supported Ni catalysts were synthesized using the beta-zeolite framework, with and without the framework Al, as a platform for dispersing Ni. The silanol nest sites of dealuminated zeolite beta provide isolated cationic Ni sites that can be reduced under relatively mild conditions to create highly dispersed metal clusters. Compared to the Ni sites present in Ni-[Al]-beta-19, Ni-[DeAl]-beta exhibit a 20-fold increase in the apparent reaction rate for C2H4 hydrogenation and is stable, with little deactivation over 16 h of catalysis. Ni K-edge X-ray absorption spectroscopy (XAS), as well as CO adsorption monitored with Fourier transform infrared spectroscopy, shows that in the oxidized Ni-[DeAl]-beta catalyst Ni reoccupies vacant silanol nests produced from dealumination. After reductive treatment, XAS shows that approximately 50% of Ni is reduced to metallic Ni, forming clusters that are approximately 1 nm in size. Scanning transmission electron microscopy images are consistent with the absence of large (>1 nm) metallic Ni clusters. These results indicate that [DeAl]-beta can be used to synthesize isolated cationic Ni sites as well as stabilize highly dispersed metal clusters that can be used as a highly active and stable C2H4 hydrogenation catalyst.

Development of highly active Cu-based CO2 hydrogenation catalysts by solution combustion synthesis (SCS): Effects of synthesis variables

This work investigates the effects of solution combustion synthesis (SCS) variables on the performance of copper-based catalysts for CO2 hydrogenation to methanol. The catalyst with a composition of 30wt%CuO50%ZnO/Al2O3 was prepared at various glycine to nitrates (G/O) ratios in the range between 0.1 and 1.23. A correlation of the effects of calcination and activation temperatures with catalytic activity was also studied. The catalyst synthesized at a G/O ratio of 0.206, calcined in air at 400 °C and activated in a stream of pure hydrogen at a temperature of 350 °C resulted in a significant improvement in the performance of the catalyst for CO2 hydrogenation. The exceptionally high catalytic performance of the catalyst was attributed to the synergic effects between small well-dispersed CuO nanoparticles and high number of induced copper phases. The highest activity of the catalyst was recorded at an operating temperature of 300 °C, a pressure of 85 bar and GHSV of 7000 h−1. The CO2 conversion, CO selectivity and methanol selectivity under these conditions were 30%, 38.60%, and 61.4%, respectively; whereas, methanol and CO yields were 0.52gMeOH/g-cat.h and 0.33gCO/g-cat.h, respectively.

A facile strategy for engineering heterostructures of Pd nanoparticle-loaded metal-organic framework nanosheets as active hydrogenation catalysts

Heterostructures of metal nanoparticle-loaded metal-organic framework (MOF) nanosheets can integrate the advantages of MOFs and nanoparticles, and thus have been widely applied as catalysts in various hydrogenation reactions. Herein, we provided a facile strategy for engineering heterostructures of Pd nanoparticle-loaded Al-TCPP(Pd) nanosheets by controlled pyrolysis in the air. The as-prepared heterostructures have been well characterized by PXRD, SEM, TEM, and XPS. In addition, these heterostructures presented promising catalytic activities in hydrogenation reactions, while their catalytic performances can be varied by the pyrolysis temperature and time, which significantly affected the uniformity and size of the Pd nanoparticles on the Al-TCPP(Pd) nanosheets. This partial pyrolysis method could be used to prepare other heterostructures of metal nanoparticle-loaded MOFs.

Biowaste carbon supported manganese nanoparticles as an active catalyst for the selective hydrogenation of bio-based aldehydes

Hydrogenation of aldehydes with heterogeneous manganese catalysts is an appealing approach for producing alcohols. In this paper, we report a novel and robust MnO/PN-800 catalyst for the hydrogenation of versatile biomass-derived platform molecules in the presence of molecular hydrogen as a reductant. The effect of catalyst concentration, the operating hydrogen pressure, and the reaction temperature on the catalyst activity was investigated in detail. Under the mild reaction conditions, the full conversion of furfuraldehyde, 5-Methyl-2-furaldehyde, and 5-hydroxymethyl-2-furaldehyde (5-HMF) to their corresponding alcohols was achieved without any by-product formation. Additionally, other aromatic aldehydes bearing fluoro, chloro, and nitro moieties were also tolerated. The fresh and spent MnO/PN-800 catalyst was thoroughly characterized using XPS, powder-XRD, HR-TEM, N2 adsorption-desorption, and Raman spectroscopy. Noteworthy, the MnO/PN-800 catalyst can be recovered by centrifugation and then reused directly in the subsequent hydrogenation reactions. Importantly the synthetic utility of this protocol up to ∼5 g-scale is realized. Finally, our novel MnO/PN-800 nanocatalyst was successfully employed for the direct synthesis of furfuryl alcohol in high yields from raw sugarcane bagasse. We believe that these findings will help to advance the manganese-catalyzed hydrogenation reactions.

Electronic Effects of Support Doping on Hydrotalcite-Supported Iridium N-Heterocyclic Carbene Complexes

The electronic effects of supports on immobilized organometallic complexes impact their activity and lifetime, yet remain poorly understood. Here we describe a systematic study of the support effects experienced by an organometallic complex immobilized on doped hydrotalcite-like materials. To that end, we describe the synthesis and characterization of the first organometallic species immobilized on a palette of doped hydrotalcites via sulfonate linkers. The organometallic species consists of iridium N-heterocyclic carbene (NHC) carbonyl complex ([Na][Ir-(NHC-Ph-SO3)2(CO)2]), a highly active molecular catalyst for transfer hydrogenation of glycerol. The hydrotalcite supports are composed of Al, Mg, and a compatible transition-metal dopant (Fe, Cu, Ni, Zn). The materials were characterized extensively by STEM, XPS, TGA, PXRD, FT-IR, N2 desorption, ICP-AES, TPD, and microcalorimetry to probe the morphology and electronic properties of the support and elucidate structure–property relationships.

Graphite-supported platinum-palladium bimetallic catalyst for aromatic hydrogenation of 4-propylphenol in aqueous ethanol solution under free-external hydrogen source

Hydrogenation of 4-propylphenol (4PP) was studied over graphite-supported platinum-palladium (Pt-Pd/G) bimetallic catalysts in aqueous ethanol solution without the use of external source. Compared to the corresponding monometallic (Pt/G and Pd/G) catalysts, the prepared Pt-Pd/G bimetallic catalysts were more active for hydrogen production and aromatic hydrogenation to 4-propyl cyclohexanone (NONE), cis- and trans-4-propyl cyclohexanols (NOLs). Pt/G was active for hydrogen production but inactive for 4PP hydrogenation, and Pd/G catalyst was active for both hydrogen production and 4PP hydrogenation. Pt-Pd/G catalysts with different platinum to palladium ratios (Pt:Pd = 1:0, 1:1, 1:2, 1:4, 1:8 and 0:1) were prepared to obtain the best composition for the ring hydrogenation. Among the bimetallic catalysts prepared, the yields of NONE and NOLs were the highest over 0.5Pt-0.5 Pd/G (0.5 wt% platinum and 0.5 wt% palladium loadings, and Pt:Pd=1:2). TEM analysis showed small (3.1–3.3 nm) metal particles dispersed on the graphite surface in the bimetallic catalysts. EXAFS analysis showed the formation of platinum core-palladium enriched shell structure of bimetallic particles. It was suggested that the high activity of Pt-Pd/G catalysts for 4PP hydrogenation in aqueous ethanol solution was caused by the formation of small platinum-palladium alloy particles on graphite surface and that palladium on the surface of particles was the active site. This work demonstrated Pt-Pd/G as highly active catalysts for aromatic hydrogenation of 4PP without the use of any external hydrogen source.

Highly dispersed platinum clusters anchored on hollow ZSM-5 zeolite for deep hydrogenation of polycyclic aromatic hydrocarbons

Deep hydrogenation of polycyclic aromatic hydrocarbons is a feasible strategy to acquire high-performance aviation fuels, in which the key is to design highly active hydrogenation catalysts. Herein, hollow ZSM-5 (HZ) and silicalite-1 (HS) zeolites with hierarchical porous architectures were manufactured through a post-alkali treatment strategy, and further supported Pt to fabricate Pt/HZ-WI, Pt/HZ-SEA and Pt/HS-SEA catalysts employing wet impregnation (WI) and strong electrostatic adsorption (SEA) methods. The SEA catalysts presented higher metal dispersion, more election-deficient Ptδ+ species and stronger spillover hydrogen ability, thus resulting in better intrinsic hydrogenation properties in the deep hydrogenation reaction of phenanthrene than the WI ones. Moreover, Pt/HZ-SEA catalyst showed the supreme catalytic activity and the lowest activation energy of 52.11 kJ·mol−1 due to more hydrogenation active sites generated by the highly dispersed Pt clusters and the accelerated diffusion of reactants via the hierarchical porous architectures. Almost 100% selectivity to the deep hydrogenation products was achieved at rather low temperature of 220 °C. The Pt/HZ-SEA also displayed outstanding activity for hydrogenation of naphthalene, acenaphthylene and fluorene and excellent sulfur resistance. Furthermore, the acidic sites in HZ zeolite were favorable to boost the formation of electron-deficient Ptδ+ species having stronger deep hydrogenation ability and intensify the additional hydrogenation route through the spillover hydrogen. Finally, the DFT calculation results further verified that the Ptδ+ substances could heighten the adsorption of polyaromatics, thereby improving the deep hydrogenation activity.

Millesimal phosphorus promoted Pd/HY for efficient hydrogenation saturation

Deep hydrogenation saturation of polycyclic aromatic hydrocarbons is of great importance for oil upgrading and chemical production. Pd/HY is an active catalyst for hydrogenation, but its acid property and metal-support interaction should be further tailored for selective deep hydrogenation saturation. In this paper, trace phosphorus in the order of one thousandth were doped into Pd/HY using a facile wet impregnation method. The influences of phosphorus doping on the physicochemical properties and catalytic performance of Pd/HY were systematically studied. Surface acidity of HY support, dispersion and electric state of Pd nanoparticles, and metal-support interaction were finely tuned by changing the doping amount of phosphorus. On the catalyst doped with 0.09 wt% phosphorus, the side reaction of hydrocracking was suppressed and deep hydrogenation saturation of naphthalene was greatly promoted for achieving a high yield of decalin. Meanwhile, doping millesimal phosphorus greatly enhanced the stability of the catalyst due to efficient inhibition of aggregation and leaching of active Pd nanoparticles in the harsh reaction environment and severe recycling process.

Rh/ZrO2@C(MIL) catalytic activity and TEM images. CO2 conversion performance and structural systematic evaluation of novel catalysts derived from Zr-MOF metallated with Ru, Rh, Pd or In

A set of novel materials, denoted M/ZrO2@C(MIL) (M = Ru, Rh, Pd & In), were prepared by thermal transformation of MIL-140C containing 10% bipyridine linkers (MIL-140C-10), to provide sites for metal coordination within the framework. These materials were transformed into active catalysts for CO2 hydrogenation when heated in a gas mixture of H2 and CO2 (3:1), at 500 °C. The thermal treatment provided high surface area catalysts with high stability and high Ru or Rh metal dispersion which were very effective for the hydrogenation of CO2 to CH4, giving a CH4 production of 3.0–3.7 mol/g Ru/h or 4.2–4.3 mol/g Rh/h (at 400 °C, 33 bar and WHSV 23 L/h/g cat.). PXRD, XPS and TEM indicated that the effective catalysts consisted of nanoparticles of Ru0 (2–5 nm) or Rh0 (6 nm) associated with larger ZrO2 nanoparticles (10–20 nm), which were dispersed upon carbonaceous ribbons. Interestingly, at 250-350 °C, Pd/ZrO2@C(MIL) yielded mainly CO rather than CH4, with some CH3OH. The CH4 and CO production were not stable at 400 °C. TEM results for this catalyst indicated Pd0 and ZrO2 nanoparticles (initially 20 nm and 10–20 nm diameter, respectively). The lower, unstable activity compared to Ru and Rh could have been due to the initially larger Pd particles and their tendency to grow in size with reaction time. In/ZrO2 has mainly been used to catalyse CH3OH production, but In/ZrO2@C(MIL) gave less CH3OH than In/monoclinic ZrO2 and was less selective. At 400 °C In/ZrO2@C(MIL) was a stable, reverse-water-gas-shift catalyst (producing 0.9 mol CO/g In/h at WHSV 20 L/g cat/h). The In was well dispersed in the ZrO2–C and of small particle size. The poor selectivity for methanol may have been due to the tetragonal phase of the ZrO2 and the low surface In concentration.

Bidentate ligand modification strategy on supported Ni nanoparticles for photocatalytic selective hydrogenation of alkynes

The design of selective and stable non-precious metal catalysts for hydrogenation of alkyne is highly desirable. In this study, L-lysine modification strategy is applied to support Ni nanoparticles, which greatly improves the stability and photocatalytic performance in the hydrogenation of phenylacetylene to styrene. The robust stability is attributed to that both amino and carboxyl groups of L-lysine can function simultaneously as the anchor, much stronger than a single group, to strongly interact with metallic Ni via N and O coordination. The high selectivity to styrene is due to that L-lysine modification results in a larger adsorption energy difference between styrene and phenylacetylene on the surface of Ni, therefore phenylacetylene is preferentially adsorbed on Ni surface. This protocol shows that the modulation of interaction between ligands and Ni is favorable to design stable, active and selective catalysts for hydrogenation of alkynes.

Highly dispersed mesoporous Cu/γ-Al2O3 catalyst for RWGS reaction

The extensive use of fossil energy leads to the wanton emission of CO2 and serious environmental problems. The resource utilization of CO2 is an effective way to solve this problem. The key of CO2 resource utilization is the design and preparation of high active CO2 hydrogenation catalyst. In this paper, supported Cu/γ-Al2O3 catalysts were prepared by wet impregnation and grinding methods, respectively. The physicochemical properties of the prepared Cu/γ-Al2O3 catalysts were characterized by XRD, BET, CO2-TPD and Quasi in-situ XPS, and the reducibility of the precursors was studied by H2-TPR. The results show that Cu content directly affects the Cu0 species crystallinity and even affects the adsorption and activation of CO2 molecules for the Cu/γ-Al2O3 catalyst. The dispersion of Cu0 species in the prepared Cu/γ-Al2O3 catalysts can be further improved by grinding method. The CO2 reaction rate on the Cu/γ-Al2O3 catalyst prepared by grinding method can be significantly increased to 2.12 × 10−5 mol/gcat/s at 400 °C.

Discovery and development of ferrocene-based tetradentate ligands for Ir-catalysed asymmetric hydrogenation of ketone

The development of highly active and enantioselective ligands and catalysts for the asymmetric hydrogenation of ketone has been the goal of synthetic chemists for more than fifty years. Herein, a series of ferrocene-based tetradentate ligands were developed and applied in Ir-catalysed asymmetric hydrogenation of ketone. The hydrolytic ring-opening of the oxazoline moiety of ligand f-amphox leads to the accidental discovery of a highly efficient and enantioselective tetradentate ligand f-phamidol which showed extraordinarily high reactivity and enantioselectivity (up to 99% yield, up to >99% ee and up to 1,000,000 TON). In addition, two types of other tetradentate ligands f-phamida and f-phamide were also synthesized and evaluated.

Reactivity of four coordinate iridium complex towards hydrogen: An experimental and computational study

Reaction of a four coordinate, 16-electron Ir complex, [Ir(iPr)4(POCOP)(PPh3)] (4) ((iPr)4(POCOP = 2,6-bis(di-isopropyl phosphinito)benzene, κ3-C6H3-1,3-[OP(iPr)2]2), with H2 resulted in an oxidative addition product, cis-dihydride complex, cis-[Ir(H)2(iPr)4(POCOP)(PPh3)] (cis-5) presumably via the intermediacy of a sigma complex, [Ir(η2-H2)(iPr)4(POCOP)(PPh3)]. The cis-dihydride complex completely isomerizes to the trans-dihydride complex trans-[Ir(H)2(iPr)4(POCOP)(PPh3)] (trans-5) under ambient conditions in about 3 h. It was found that the steric and electronic features on the iridium center have significant influence on the approach of H2 onto the metal center followed by oxidative addition and isomerization. The isomerization process was studied in detail and all the mechanistic aspects have been elucidated using a combination of both experimental work and computation. The cis-dihydride complex isomerizes to the trans-dihydride by compensating the trans influence of the strongly trans-directing hydride ligand. A mechanism involving the exchange of the position of PPh3 with a hydride ligand cis to itself via PPh3 dissociation and re-coordination thereby resulting in the formation of the trans-dihydride complex, has been proposed for the isomerization. The cis-dihydride was found to be a highly active catalyst for hydrogenation of ethylene. A competing reactivity study of cis-dihydride between isomerization versus insertion of C2H4 into the Ir—H bond, was studied experimentally and computationally.

MIL-100(Fe) Supported Pt-Co Nanoparticles as Active and Selective Heterogeneous Catalysts for Hydrogenation of 1,3-Butadiene.

Superior catalytic performance for selective 1,3‐butadiene (1,3‐BD) hydrogenation can usually be achieved with supported bimetallic catalysts. In this work, Pt−Co nanoparticles and Pt nanoparticles supported on metal–organic framework MIL‐100(Fe) catalysts (MIL=Materials of Institut Lavoisier, PtCo/MIL‐100(Fe) and Pt/MIL‐100(Fe)) were synthesized via a simple impregnation reduction method, and their catalytic performance was investigated for the hydrogenation of 1,3‐BD. Pt1Co1/MIL‐100(Fe) presented better catalytic performance than Pt/MIL‐100(Fe), with significantly enhanced total butene selectivity. Moreover, the secondary hydrogenation of butenes was effectively inhibited after doping with Co. The Pt1Co1/MIL‐100(Fe) catalyst displayed good stability in the 1,3‐BD hydrogenation reaction. No significant catalyst deactivation was observed during 9 h of hydrogenation, but its catalytic activity gradually reduces for the next 17 h. Carbon deposition on Pt1Co1/MIL‐100(Fe) is the reason for its deactivation in 1,3‐BD hydrogenation reaction. The spent Pt1Co1/MIL‐100(Fe) catalyst could be regenerated at 200 °C, and regenerated catalysts displayed the similar 1,3‐BD conversion and butene selectivity with fresh catalysts. Moreover, the rate‐determining step of this reaction was hydrogen dissociation. The outstanding activity and total butene selectivity of the Pt1Co1/MIL‐100(Fe) catalyst illustrate that Pt−Co bimetallic catalysts are an ideal alternative for replacing mono‐noble‐metal‐based catalysts in selective 1,3‐BD hydrogenation reactions.

Micro-/mesopores confined ultrasmall Cu nanoparticles in SBA-15 as a highly efficient and robust catalyst for furfural hydrogenation to furfuryl alcohol

The main difficulty in the liquid phase furfural hydrogenation process is the control of the selectivity to the target product among the possible ones. When copper catalysts are used, they often suffer from low stability in liquid medium. Herein, we report a general preparation method based on glycine-assisted in situ autocombustion to synthesize Cu supported catalysts. This method could lead to highly active, selective and stable catalysts in the liquid phase furfural hydrogenation. The resulting 10Cu-SBA-GLY catalyst (10 wt% Cu on SBA-15) could achieve a complete conversion of furfural to furfuryl alcohol under mild reaction conditions. Further, neither Cu leaching nor Cu NPs sintering were observed during the 5-run recycling tests, and the loss of conversion and selectivity stays below 3%. Such exceptional features make these Cu-SBA-GLY catalysts potential for the industrial applications not only in furfural hydrogenation but also in other hydroconversion processes.

Restructuring Ni/Al2O3 by addition of Ga to shift product selectivity in CO2 hydrogenation: The role of hydroxyl groups

Ni/Al2O3 is an active catalysts for CO2 hydrogenation to both CH4 and CO. By doping with Ga, we succeeded in shifting the selectivity of these catalysts almost completely toward CO. In-situ IR spectroscopy studies showed that the catalyst activity is directly related to the concentration of surface hydroxyl groups that are responsible for the adsorption of CO2 and the formation of intermediate bicarbonates and formates on the catalyst surface. The addition of Ga improved the Ni dispersion which was concomitant with the formation of a Ni-Ga layer on the surface of alumina, thereby reducing the surface hydroxyl concentration. The reduced and weakened interaction between the intermediate products, i.e. bicarbonates and formates, and the catalyst surface, increased the CO selectivity from ∼40 % to 98 %.

Establishing tungsten carbides as active catalysts for CO2 hydrogenation.

Molybdenum carbides are promising catalysts for the reverse water-gas shift (RWGS) reaction, and we aim to understand if similar performance can be observed across the library of transition metal carbides. Although tungsten and molybdenum carbides exhibit similar catalytic properties for hydrogenation reactions, tungsten carbide has not been thoroughly evaluated for CO2 hydrogenation. We hypothesize that the extreme synthesis conditions necessary for carburizing tungsten can cause sintering, agglomeration, and carbon deposition, leading to difficulty evaluating the intrinsic activity of tungsten carbides. In this work, tungsten is encapsulated in silica to preserve particle size and demonstrate correlations between the active phase composition and RWGS performance.

Development of Active Cu-Based Catalysts for Co2 Hydrogenation to Methanol

Development of Active Cu-Based Catalysts for Co2 Hydrogenation to Methanol

Ultrafine PdCo bimetallic nanoclusters confined in N-doped porous carbon for the efficient semi-hydrogenation of alkynes.

Semi-hydrogenation of alkynes to prepare alkenes is an important reaction in the petrochemical and fine chemical industries. The use of conventional Pd nanoparticle-based catalysts is limited by alkyne over-hydrogenation and low Pd utilization. In this study, a nitrogen-doped mesoporous carbon material (m-NC), which was rich in defect sites after Zn volatilization, was fabricated by the carbonization of ZIF-8. Ultrafine PdCo bimetallic nanoclusters with Co atom-modified Pd active site electronic and compositional structure were highly dispersed and confined in m-NC. As-obtained Pd0.43Co1/m-NC was used for the semi-hydrogenation of alkynes and it exhibited high selectivity with high conversion under mild reaction conditions. Pd0.43Co1/m-NC also exhibited excellent stability in leaching tests and maintained its catalytic activity for at least nine reaction cycles. The highly dispersed active sites in Pd0.43Co1/m-NC served as the active sites for the catalytic semi-hydrogenation of alkynes; as a regulator, the second metal Co effectively improved selectivity, and m-NC endowed the catalyst with excellent stability. The research work presented here may provide a foundation for the design of highly active, selective, and stable Pd-based bimetallic catalysts for selective hydrogenation.

Highly active heterogeneous hydrogenation catalysts prepared from cobalt complexes and rice husk waste

Highly active heterogeneous catalysts for the hydrogenation of nitro compounds were made by pyrolysis of rice husk waste impregnated with cobalt complexes followed by base-treatment. The catalysts show high selectivity and broad substrate scope.