Active Hydrogenation Catalysts Research Articles

КАТАЛИЗ ГИДРИРОВАНИЯ АРОМАТИЧЕСКИХ СОЕДИНЕНИЙ: ИСТОРИЯ И СОВРЕМЕННОЕ СОСТОЯНИЕ. ЧАСТЬ 2. ГИДРИРОВАНИЕ ПОЛИЯДЕРНЫХ АРОМАТИЧЕСКИХ УГЛЕВОДОРОДОВ, АЗОТ- И КИСЛОРОДЗАМЕЩЕННЫХ АРЕНОВ

The review is devoted to hydrogenation processes of aromatic substrates differing in reactivity using catalysts of different activity. The global trend in this area is the search for more active and selective heterogeneous catalysts for hydrogenation of the aromatic ring, both for industrial processes and in laboratory practice. An analysis of literature data on the hydrogenation of polynuclear aromatic hydrocarbons, phenol, aniline and their derivatives, as well as arenes substituted with a functional group, is presented. Various types of catalysts for the hydrogenation of an aromatic ring, the patterns of the process depending on the structure of the substrate and reaction conditions, the nature of the active phase and the catalyst support are considered.

Multi-metal catalysts for selective furfural hydrogenation: Toward biomass valorisation

The research presented here focuses on the design of non-noble transition metal-based bimetallic catalysts, prepared via a green sol-gel process (the urea-glass route), which leads to well-defined (in composition and size) and crystalline nanoparticles, with high surface area. The potential of these tailor-made catalysts for biomass-related model reactions is also presented. In particular, carbon supported Ni, Ni3Fe, Ni0.5Fe0.5, Ni0.5Fe0.5/Fe3C and Ni0.35Fe0.65/NiFe2O4 nanoparticles were synthesized and tested as-prepared, with no need for post-synthesis purification, activation, or co-catalysts addition. Results showed that these catalysts are active in the liquid-phase hydrogenation of furfural (FUR), with almost full conversion with Ni° catalyst, at 170 °C after 22 h, under 4 MPa hydrogen pressure, obtaining the highest yield towards tetrahydrofurfuryl alcohol (THFA) of 85%. More interesting, the incorporation of Fe, to form NiFe alloys, modifies the hydrogenating capacity of the catalyst, provoking a change in the selectivity pattern, from tetrahydrofurfuryl alcohol (THFA), obtained as the only product with Ni° nanoparticles, to furfuryl alcohol (FFA). Thus, high FFA and THFA yields can be obtained by modifying the nature of the metallic phase of samples synthesized with the urea-glass route, demonstrating the potential of this methodology for the preparation of active and selective catalysts for liquid-phase FUR hydrogenation.

Novel Metallomacrocyclic Carboxamide Mn(II) Complexes as Efficient Catalysts for the Transfer Hydrogenation of Ketones

AbstractHerein, we present the first metallomacrocyclic Mn(II) complexes as efficient catalysts for the transfer hydrogenation of ketones. The dinuclear Mn(II) complexes [Mn2(L1–L4)2Cl2] (Mn1–Mn4), were synthesised in good yields by reacting MnCl2 ⋅ 4H2O with the ligands N,N′‐(1,4‐phenylene)dipicolinamide (L1), N,N′‐(1,2‐phenylene)dipicolinamide (L2), N,N′‐(4‐methoxy‐1,2‐phenylene)dipicolinamide (L3) and N,N′‐(4,5‐dimethyl‐1,2‐phenylene)dipicolinamide (L4). Structural characterization of the resulting Mn(II) complexes was achieved using FT‐IR spectroscopy, mass spectrometry, magnetic moment measurements, elemental analysis, and single‐crystal X‐ray diffraction for Mn2. The solid‐state structure of complex Mn2 reveals a dinuclear Mn(II) core, in which the metal coordination sphere consists of two bidentate, K2(N−O) bridging L2 units and two chlorido ligands to give a distorted octahedral geometry. The Mn(II) complexes (Mn1–Mn4) were quite active catalysts for the transfer hydrogenation of ketones displaying turnover numbers (TON) of up to 2633, which is comparable to those of well‐established Mn(I) catalysts. The new Mn(II) complexes also efficiently hydrogenated a number of aromatic, heterocyclic, functionalized and aliphatic ketones. More significantly, cheaper, and readily available hydrogen sources like ethanol also gave decent catalytic activities in the transfer hydrogenation reactions.

CO2 hydrogenation using MOFs encapsulated PdAg nano-catalysts for formate production

Catalytic hydrogenation of CO2 for the production of formic acid/formate, a valuable commodity and renewable hydrogen carrier, is a promising strategy to achieve an economic andsustainable CO2-mediated hydrogen energy cycle. The rational design of highly active and stable heterogeneous catalysts for CO2 hydrogenation in gas–liquid-solid phase still remains challenging. In this work, we report a series of dual-function catalysts namely PdAg@MIL-101-PEI, where PdAg alloy nanoparticles (NPs) for hydrogen activation and dissociation are encapsulated into MIL-101 supports tethered with CO2 adsorption agent polyethyleneimine (PEI). The optimal PdAg@MIL-101-PEI catalyst displays exceptional performance for CO2 hydrogenation, affording a high turnover number (TON) of 4968 at 120 °C under 8 MPa in 2 h. Thermodynamic and kinetic studies illustrate that Ag incorporation and PEI functionalization dramatically reduce the activation energy barrier of PdAg@MIL-101-PEI catalyst for CO2 hydrogenation. Furthermore, the optimal PdAg@MIL-101-PEI catalyst demonstrates outstanding structural stability and reusability over multiple catalytic cycles. We also propose a reaction mechanism for CO2 hydrogenation through in situ DRIFTS study.

Construction of Highly Active and Selective Molecular Imprinting Catalyst for Hydrogenation.

Surface molecular imprinting (MI) is one of the most efficient techniques to improve selectivity in a catalytic reaction. Heretofore, a prerequisite to fabricating selective catalysts by MI strategies is to sacrifice the number of surface-active sites, leading to a remarkable decrease of activity. Thus, it is highly desirable to design molecular imprinting catalysts (MICs) in which both the catalytic activity and selectivity are significantly enhanced. Herein, a series of MICs are prepared by sequentially adsorbing imprinting molecules (nitro compounds, N) and imprinting ligand (1,10-phenanthroline, L) over the copper surface of Cu/Al2O3. The resulting Cu/Al2O3-N-L MICs not only offer promoted catalytic selectivity but also enhance catalytic activity for nitro compounds hydrogenation by an creating imprinting cavity derived from the presorption of N and forming new active Cu-N sites at the interface of the copper sites and L. Characterizations by means of various experimental investigations and DFT calculations disclose that the molecular imprinting effect (promoted activity and selectivity) originates from the formation of new active Cu-N sites and precise imprinting cavities, endowing promoted catalytic selectivity and activity on the hydrogenation of nitro compounds.

Acetone hydrogenation over face-centered cubic and hexagonal close-packed cobalt

Acetone hydrogenation is employed for investigating the structure sensitivity of H2 activation over cobalt catalysts while the produced isopropanol garners increasing interest in the sustainable energy context e.g. as H2 storage material and fuel for direct fuel cells. Both hexagonal close-packed (hcp) and face-centered cubic (fcc) Co can produce isopropanol with 100% selectivity below 150 °C with the reaction proceeding almost ten times faster over hcp Co. Hydrogenation rates are even higher over an hcp Co/Co3O4 composite which remains highly selective to isopropanol despite that Co3O4 yields mostly mesityl oxide and related products. The superior performance of hcp Co and its composite are attributed to efficient generation of atomic H on the metal and the presence of stronger sites for acetone activation on XRD-amorphous phases that are formed during reduction of the Co3O4 precursor at 250 °C and 400 °C. These findings provide insight into the optimum structural design of highly active and selective low-temperature cobalt hydrogenation catalysts.

Highly Selective Conversion of Carbon Dioxide to Methanol through a Cu−ZnO−Al2O3−ZrO2/Cu−MOR Tandem Catalyst

AbstractMethanol formation from CO2 hydrogenation attracts great attention in view of utilization of carbon resources. However, CO2 transformation to methanol is challenging because of the thermodynamic equilibrium restriction and water‐caused catalyst deactivation. It is desired, therefore, to develop highly active, selective and stable catalysts for CO2 hydrogenation to methanol. Herein, we propose a novel tandem catalyst composed of Cu−ZnO−Al2O3−ZrO2 (CZAZ) and Cu−MOR for highly selective conversion of CO2 to methanol. During CO2 hydrogenation by the CZAZ catalyst, the by‐product methane is continuously transformed to methanol through reaction with water via the Cu−MOR catalyst, thus enhancing CO2 conversion and methanol selectivity. Under mild reaction conditions (200 °C and 3.0 MPa), high CO2 conversion (40.7 %) and methanol selectivity (97.6 %) are achieved, outperforming state‐of‐the‐art CO2 hydrogenation catalysts. Further, water‐caused deactivation of the catalyst through aggregation and densification is suppressed owing to water consumption via methane oxidation to methanol, validating a high CZAZ/Cu−MOR tandem catalyst stability.

A Highly Active and Reusable Multicomponent high Entropy Metal Oxide Catalyst for Nitroarenes Hydrogenation

It is well known that multicomponent catalysts can improve catalytic performance, however their rational design and precise control of catalytic activities by varying the composition of the elements is challenging. Herein, we present a facile and scalable synthetic strategy for production of senary and septenary metal oxide nanoparticles with a chemical composition of MSbOx and MSb2Ox (M: Fe, Ni, Co, Cu, and Zn). All samples were formed in a tetragonal crystal structure with space group 136 and crystallographic symmetry P42/mnm while the details of their constituent unit cells are different, belonging to rutile or trirutile structures. These nanocomposites have an oxygen vacancy-rich construction with uniform elemental distributions that produce various surface functionalities. They showed instantaneous hydrogenation catalytic performance for reduction of 4-nitrophenol to 4-aminophenol at room temperature. Among our samples, the senary catalyst with MSbOx chemical composition showed better durability and reusability owning to its morphological and microstructural properties. It showed 100% conversion of 4-nitrophenol to 4-aminophenol within 4 min at the 18th run without any by-products.

COMPARATIVE HYDROGENATION OF BENZENE DEPOSITED BY RHODIUM AND PLATINUM CATALYSTS

Rhodium and platinum, as the most active catalysts for hydrogenation of the aromatic ring, were applied to γ-Al2O3 under comparative conditions and their activities during hydrogenation of benzene in hexane were compared. It is shown that under the studied conditions, rhodium exhibits greater activity than platinum during the hydrogenation of benzene in hexane at 80 oC and 40 atm. It is more active than platinum when hydrogenating benzene in hexane at 80o C and 40 atm.

Pd Nanoparticles Supported on N-Incorporated Hybrid Organosilica as an Active and Selective Low-Temperature Phenol Hydrogenation Catalyst

A heterogeneous Pd-NPMO hybrid-silica catalyst is synthesized and its application for aqueous phase selective hydrogenation of phenol to cyclohexanone at near ambient temperature (40 °C) and under atmospheric hydrogen pressure is demonstrated. The homogeneously distributed Pd nanoparticles on N-bridged hybrid mesoporous organosilica showed remarkable activity and selectivity for cyclohexanone compared to the unmodified Pd-SBA-15 catalyst. Control experiments strongly claim the role of nitrogen domains in the organic framework of hybrid silica support in stabilizing small Pd nanoparticles and possibly modifying the Pd sites responsible for catalysis to activate the substrate molecules in water. The hybrid silica catalyst was stable and reused several times without any significant drop-in activity, proving the heterogeneity of the bifunctional Pd catalyst. Based on the density functional theory study and experimental interventions, a possible reaction mechanism for the low-temperature phenol hydrogenation explaining the role of organic domains in the hybrid-silica framework is proposed.

A Highly Active Nickel Catalyst for the Selective Hydrogenation of Functionalized Nitroarenes

AbstractThe catalytic hydrogenation of nitroarenes using hydrogen gas as reducing agent to form substituted aniline derivates is an important reaction in industry and academic research. Here, we report on the nitroarene hydrogenation capability of a nanostructured nickel catalyst synthesized from a nickel salen complex and a commercially available porous silica support. Our catalyst allows the selective hydrogenation of nitroarenes under mild conditions while tolerating various functional groups and hydrogenation‐sensitive examples such as iodine, nitrile or olefinic groups. The use of the nickel salen complex as metal precursor is crucial for the high activity and selectivity observed.

AuFe3@Pd/γ-Fe2O3 Nanosheets as an In Situ Regenerable and Highly Efficient Hydrogenation Catalyst

Heterogenous Pd catalysts play a pivotal role in the chemical industry; however, it is plagued by S2- or other strong adsorbates inducing surface poisoning long term. Herein, we report the development of AuFe3@Pd/γ-Fe2O3 nanosheets (NSs) as an in situ regenerable and highly active hydrogenation catalyst. Upon poisoning, the Pd monolayer sites could be fully and oxidatively regenerated under ambient conditions, which is initiated by •OH radicals from surface defect/FeTetra vacancy-rich γ-Fe2O3 NSs via the Fenton-like pathway. Both experimental and theoretical analyses demonstrate that for the electronic and geometric effect, the 2-3 nm AuFe3 intermetallic nanocluster core promotes the adsorption of reactant onto Pd sites; in addition, it lowers Pd's affinity for •OH radicals to enhance their stability during oxidative regeneration. When packed into a quartz sand fixed-bed catalyst column, the AuFe3@Pd/γ-Fe2O3 NSs are highly active in hydrogenating the carbon-halogen bond, which comprises a crucial step for the removal of micropollutants in drinking water and recovery of resources from heavily polluted wastewater, and withstand ten rounds of regeneration. By maximizing the use of ultrathin metal oxide NSs and intermetallic nanocluster and monolayer Pd, the current study demonstrates a comprehensive strategy for developing sustainable Pd catalysts for liquid catalysis.

Lithium Aluminium Hydride and Metallic Iron: A Powerful Team in Alkene and Arene Hydrogenation Catalysis

AbstractAlkenes that normally do not react with LiAlH4 (3‐hexene, cyclohexene, 1‐Me‐cyclohexene), can be reduced to the corresponding alkanes by a mixture of LiAlH4 and Fe0 (the iron was activated by Metal‐Vapour‐Synthesis). This alkene‐to‐alkane conversion with a stoichiometric quantity of LiAlH4/Fe0 does not need quenching with water or acids, implying that both H's originate from LiAlH4. The LiAlH4/Fe0 combination is also a remarkably potent cooperative catalyst for hydrogenation of multi‐substituted alkenes and benzene or toluene. An induction period of circa two hours and the minimally required temperature of 120 °C, suggests that the actual catalyst is a combination of Fe0 and the decomposition product of LiAlH4 (LiH and Al0). A thermally pre‐activated LiAlH4/Fe0 catalyst did not need an induction time and is also active at room temperature and 1 bar H2. A combination of AliBu3 and Fe0 is an even more active hydrogenation catalyst. Without pre‐activation, tetra‐substituted alkenes like Me2C=CMe2 and toluene could be fully hydrogenated.

Lithium Aluminium Hydride and Metallic Iron: A Powerful Team in Alkene and Arene Hydrogenation Catalysis.

Alkenes that normally do not react with LiAlH4 (3-hexene, cyclohexene, 1-Me-cyclohexene), can be reduced to the corresponding alkanes by a mixture of LiAlH4 and Fe0 (the iron was activated by Metal-Vapour-Synthesis). This alkene-to-alkane conversion with a stoichiometric quantity of LiAlH4 /Fe0 does not need quenching with water or acids, implying that both H's originate from LiAlH4 . The LiAlH4 /Fe0 combination is also a remarkably potent cooperative catalyst for hydrogenation of multi-substituted alkenes and benzene or toluene. An induction period of circa two hours and the minimally required temperature of 120 °C, suggests that the actual catalyst is a combination of Fe0 and the decomposition product of LiAlH4 (LiH and Al0 ). A thermally pre-activated LiAlH4 /Fe0 catalyst did not need an induction time and is also active at room temperature and 1 bar H2 . A combination of AliBu3 and Fe0 is an even more active hydrogenation catalyst. Without pre-activation, tetra-substituted alkenes like Me2 C=CMe2 and toluene could be fully hydrogenated.

Highly active MgO catalysts for hydrogenation of levulinic acid to γ-valerolactone using formic acid as the hydrogen source

This study presents an evaluation of catalytic performance of unsupported simple oxide catalysts with varying acid-base properties for the vapor phase hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) using formic acid (FA) in an aqueous medium. Among the different oxides tested MgO catalyst is found to be highly active. Between the MgO prepared by different methods and commercially obtained, the MgO-UBE showed 100% LA conversion and 100% selectivity to GVL at 270°C. The MgO-UBE catalyst favorably allowed the production of γ-valerolactone in the presence of 50 wt% water relative to the amount of a mixture of levulinic acid and formic acid. Based on the catalytic activity and characterization results, it was concluded that the presence of Mg (OH)2 and a higher number of Lewis acid-base pair sites, Mg2+LCO2−LC are needed to achieve high LA conversion and selectivity to GVL.

Hydrogenation of Carbon Monoxide in the Liquid Phase: Influence of the Synthetic Methods on Characteristics and Activity of Hydrogenation Catalysts

Oxygenate fuels are a promising solution to urban air pollution, reducing soot emissions by big margins. Formaldehyde is a major building block for the synthesis of oxygen-rich fuels. Herein we report the synthesis, characterisation and testing of ruthenium on alumina catalysts for the methanol-mediated CO hydrogenation towards oxygenates with the formaldehyde oxidation state. We varied the synthesis parameters and could see interesting correlation between synthesis parameters, final metal loading, crystallite sizes and catalyst activity. The catalysts were tested in a high-pressure three-folded reactor plant in the CO hydrogenation in methanolic media. Interesting relationships between catalyst synthesis, structure and activity could be gained from these experiments.

Highly active and stable MoS2-TiO2 nanocomposite catalyst for slurry-phase phenanthrene hydrogenation

MoS2-TiO2 nanocomposite catalysts with Janus structure were synthesized via facile one-step solvothermal method. X-ray diffraction, high resolution transmission electron microscope, NO chemisorption and X-ray photoelectron spectroscopy were applied to characterize the composition and nanostructure of the MoS2-TiO2 nanocomposite catalysts. Experimental results revealed that the MoS2-TiO2 nanocomposite catalysts with Janus structure were composed of MoS2 layers (few stacked layers of 1–3 and short slabs of 2–10 nm) and TiO2 nanoparticles (10–15 nm), which have strong MoS2-TiO2 interaction with transferring electrons from TiO2 to MoS2. Catalytic performance of MoS2-TiO2 nanocomposite catalysts for phenanthrene hydrogenation was investigated and compared with that of MoS2 catalyst in an autoclave reactor with high temperature and high pressure. The phenanthrene conversion over the MoS2-TiO2 nanocomposite catalyst with MoS2 content of 15.0 wt% (MoS2-TiO2-15) can reach 91.6%, which was much higher than 50.4% for MoS2 catalyst and 76.8% for conventional supported MoS2/TiO2-15 catalyst. After 7 cycles of phenanthrene hydrogenation reaction, the phenanthrene conversion over MoS2-TiO2-15 nanocatalyst remained at 68.6%, while the phenanthrene conversion over MoS2 catalyst was reduced to only 25.4%. The MoS2-TiO2 nanocomposite catalysts exhibit significantly enhanced catalytic activity and stability for slurry phase hydrogenation. The enhanced catalytic activity originates from the exposure of abundant coordinatively unsaturated Mo atoms. The enhanced stability results from the Janus structure with stable MoS2-TiO2 interaction and Mo–O–Ti bonds, which anchor MoS2 layers on the surface of TiO2 nanoparticles to avoid the curling, folding and agglomeration of MoS2 layers. This is an important finding on slurry phase catalytic hydrogenation performances of MoS2-based nanocomposite catalysts with Janus structure. Shedding light on the research of Janus nanocomposite catalysts in catalytic hydrogenation is significantly crucial for the development of effective and stable hydrogenation catalysts.

Trace ultrafine Ru nanoparticles on Ni/Al hydrotalcite-derived oxides supports as extremely active catalysts for N-ethylcarbazole hydrogenation

Liquid organic hydrogen carriers (LOHCs) is a promising hydrogen storage technology and has become a hot issue. However, there is still a shortage of LOHCs hydrogenation catalysts that can balance cost and catalytic performance. In this work, a series of Ni/Al hydrotalcite-derived oxides (LDOs) were prepared with different Ni/Al ratios and preparation methods, on which trace ultrafine Ru nanoparticles (0.5 wt%, 1 wt%, 1.5 wt%) were supported. The activities were investigated for the hydrogenation of N-ethylcarbazole (NEC), one of the most promising liquid organic hydrogen carriers. Characterizations including XRD, XPS, SEM, TEM and H2-TPR indicate the composition of Ni/Al-LDOs and reveal three kinds of Ni/Al interactions existed in Ni/Al-LDOs. The influences of Ni-Al interactions on the size of Ru NPs supported on Ni/Al-LDOs and on the NEC hydrogenation activity were also explored. The results show that 1.5 wt% Ru-Ni1Al2-LDO300 has the best catalytic performance for NEC hydrogenation, with which can achieve up to 5.5 wt% hydrogen absorption at 150℃ and 8 MPa for 12 min, and the yield of 12H-NEC can reach 100 % for 60 min. In other words, the catalytic performance of 1.5 wt% Ru supported catalyst is superior to 5 wt% Ru/Al2O3 catalyst commonly used for NEC hydrogenation. This work provides a new idea for preparing catalysts with low cost and high performance by tuning the structure of Ni/Al-LDO supports and the size of Ru NPs.

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.

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.