Catalysts For Hydrogenation Research Articles

Highly selective CuO-ZnO@Cu-MOR catalysts prepared by ultrafast solid processing for carbon dioxide hydrogenation to methanol

The conversion of CO2 into methanol has emerged as a promising strategy for addressing climate change and optimizing the utilization of carbon resources. Conventional synthesis methods for Cu-based catalysts, such as co-precipitation, necessitate the consumption of substantial amounts of solvent and meticulous control over preparation conditions, while also being susceptible to deactivation by water during hydrogenation. Therefore, it is crucial to develop a catalyst that can be readily synthesized and exhibits outstanding performance and durability. In this study, we present an ultrafast (only 20 min), solid-phase grinding approach to fabricate CuO-ZnO@Cu-MOR catalysts for CO2 hydrogenation to methanol. The resulting catalysts were comprehensively characterized using XRD, XPS, H2-TPR, NH3-TPD, SEM, HRTEM, and In-situ-FTIR techniques. Notably, the CuO-ZnO@Cu-MOR catalysts with a distinctive capsule-like structure displayed a high catalytic performance for CO2 hydrogenation. The byproducts of methane and water produced by the CO2 hydrogenation process were able to be further converted to methanol through Cu-MOR, leading to a significant enhancement of the methanol selectivity (95.6 %) and CO2 conversion (22.8 %). Moreover, a long-term test lasting 300 h demonstrated constant catalytic performances and superior durability.

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.

Selective Hydrogenation of Aldehydes under Syngas Using CeO2-Supported Au Nanoparticle Catalyst.

Chemoselective hydrogenation of aldehydes to alcohols is of importance in synthetic chemistry. Here, we report a reusable CeO2-supported Au nanoparticle catalyst for the selective hydrogenation of aldehydes using syngas as the hydrogen source for which CO in syngas works as a site blocker to prevent side reactions. In particular, the hydrogenation of aldehydes with an easily reducible alkene, alkyne, or halogen moiety under syngas gave the corresponding alcohols with high selectivity, while the hydrogenation under pure hydrogen resulted in overreduction or dehalogenation. Of particular interest is that CO works as a site blocker but does not affect the hydrogenation rate significantly. A potential application of the present catalyst system was demonstrated by the conversion of terminal alkenes to alcohols via a one-pot hydroformylation/hydrogenation sequence.

Deciphering Local Structural Complexity in Zn/Ga-ZrO2 CO2 Hydrogenation Catalysts.

In the last few decades, massive effort has been expended in heterogeneous catalysis to develop new materials presenting high conversion, selectivity, and stability even under high-temperature and high-pressure conditions. In this context, CO2 hydrogenation is an interesting reaction where the catalyst local structure is strongly related to the development of an active and stable material under hydrothermal conditions at T/P > 300 °C/30 bar. In order to clarify the relationship between catalyst local ordering and its activity/stability, we herein report a combined laboratory and synchrotron investigation of aliovalent element (Ce/Zn/Ga)-containing ZrO2 matrixes. The results reveal the influence of similar average structures with different short-range orderings on the catalyst properties. Moreover, a further step toward the comprehension of the oxygen vacancy formation mechanism in Ce- and Ga-ZrO2 catalysts is reported. Finally, the reported results illustrate a robust method to guide local structure determination and ultimately help to avoid overuse of the "solid solution" definition.

Unlocking the Potential of Cu/Ti3C2Tx MXene Catalyst in Plasma Catalytic CO2 Hydrogenation

Plasma catalytic CO2 hydrogenation has emerged as a promising approach for converting CO2 into valuable chemicals such as CO, offering a potential solution to mitigate greenhouse gas emissions. In this study, we investigate the synergistic effect between plasma and a Cu/Ti3C2Tx MXene catalyst for CO2 hydrogenation via the reverse water gas shift (RWGS) reaction in a dielectric barrier discharge (DBD) reactor. Our findings reveal a significant enhancement in CO2 conversion (33.1%) and CO yield (31.9%) when using the Cu/Ti3C2Tx catalyst compared to plasma alone or with a Ti3C2Tx foam. Plasma treatment creates unsaturated Ti sites on the Ti3C2Tx surface, dramatically improving CO2 adsorption and activation, while Cu nanoparticles significantly enhances the activation and dissociation of H2 molecules on the catalyst surface. These surface adsorbed hydrogen species readily hydrogenate adsorbed CO2 molecules through the Langmuir-Hinshelwood mechanism. Furthermore, these surface hydrogen species can also participate in the conversion of gas-phase CO2 molecules through the Eley-Rideal pathway. This work sheds light on the synergistic plasma catalytic mechanism and provide insights for optimizing CO2 hydrogenation processes using MXene catalysts.

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

Functionalized ionic liquid coatings in the Pd-catalyzed selective hydrogenation of acetylene in ethylene-rich feeds

This study explores the tuning of a Pd/Al2O3 hydrogenation catalyst for the selective removal of trace acetylene from ethylene-rich feeds by coating the catalyst with non-functionalized and functionalized ionic liquids (denoted as SCILL and Advanced SCILL materials, respectively). These materials were tested in an automated continuous hydrogenation rig converting 3300 ppm of acetylene in excess ethylene, a gas mixture mimicking a technical front-end steam cracker feed composition. While the sulfonic-acid-functionalized IL coating resulted in a highly active but very unselective catalyst converting mainly ethylene to ethane, an Advanced SCILL catalyst prepared from a nitrile-functionalized IL reduced the acetylene concentration down to less than 1 ppm, while leaving over 99% of the ethylene untouched. We also examined the potential transformations of the IL layer under reaction conditions by means of 1H NMR. Except for a ketone-functionalized IL, which was inherently labile, all tested ILs primarily underwent C2-ethylation or remained unaltered. Our findings highlight the great potential of functionalized ILs in modifying heterogeneous hydrogenation catalysts.

Regeneration of copper catalysts mediated by molybdenum-based oxides

Cu catalysts, known for their unparalleled catalytic capabilities due to their unique electronic structure, have faced inherent challenges in maintaining long-term effectiveness under harsh hydrogenation conditions. Here, we demonstrate a molybdenum-mediated redispersion behavior of Cu under high-temperature oxidation conditions. The oxidized Cu nanoparticles with rich metal-support interfaces tend to dissolve into the MoO3 support upon heating to 600 °C, which facilitates the subsequent regeneration in a reducing atmosphere. A similar redispersion phenomenon is observed for Cu nanoparticles supported on ZnO-modified MoO3. The modification of ZnO significantly improves the performance of the Cu catalyst for CO2 hydrogenation to methanol, with the high activity being well maintained after four repeated oxidation-reduction cycles. In situ spectroscopic and theoretical analyses suggest that the interaction involved in the formation of the copper molybdate-like compound is the driving force for the redispersion of Cu. This method is applicable to various Mo-based oxide supports, offering a practical strategy for the regeneration of sintered Cu particles in hydrogenation applications.

Nitrogen species from Spirulina platensis derived bio-oil enhance catalytic activity of cobalt catalysts for hydrogenation

High nitrogen content in Spirulina platensis-derived bio-oil is a highly undesirable feature in upgrading of bio-oil to biofuel via hydrodeoxygenation. However, the nitrogen species could be potentially used as dopant for tailoring the catalytic behaviors of metallic sites in heterogeneous catalysts. In this study, the nitrogen species in the bio-oil from hydrothermal carbonization (HTC) of Spirulina platensis was used to modify Co-based catalyst for enhancing their catalytic activity for hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the introduction of N species not only promoted dispersion of Co particles via formation of Co–N sites, but also generated extra pores and significantly increased H2 uptake. The abundant Co–N sites, high dispersion of Co and higher surface area of N-doped catalyst (CoFeAl–N) jointly contributed to the enhanced catalytic activity for hydrogenation of o-CNB, achieving the yield of 90.3% for o-chloroaniline (o-CA) and lowering the activation energy from 63.0 kJ mol−1 (with N-free CoFeAl catalyst) to 55.1 kJ mol−1. The effectiveness of introducing nitrogen for enhancing catalytic activity for hydrogenation of o-CNB was also confirmed in the experiments for doping Co/Al2O3 (prepared via impregnation) and CoAl (prepared via co-precipitation) catalysts with the Spirulina platensis derived bio-oil.

Facile synthesis of Cu@Ag/SiO2 catalysts for the selective hydrogenation of dimethyl oxalate to methyl glycolate

A promising route for producing biodegradable polyglycolic acid material from syngas has garnered increasing attentions. In this route, one of the pivotal issues is developing favorable catalysts for semi-hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG). Silver catalysts were reported to be effective but suffered from the high cost. Herein, we prepared small-sized Cu@Ag/SiO2 catalysts with appropriate Ag/Cu ratios by a facile wet impregnation method. This core–shell structure facilitated the intermetallic electronic transference from Cu to Ag. The surface exposure of electron-rich silver species could promote the catalytic activity and MG desorption in the DMO hydrogenation, which achieved high efficiency without compromising the MG selectivity. The optimal catalyst with Ag/Cu mass ratio of 3/2 displayed excellent space time yield towards MG of 47.3 g·gAg−1·h−1. These insights could offer a potential strategy to reduce the silver-based catalyst cost for the semi-hydrogenation of DMO to MG.

Catalytic hydrogenation of CO2 to DME on surface Cu via highly efficient electron redistribution at the Cu0/Cu+ interface

The activity of copper-based bifunctional catalysts for CO2 hydrogenation to dimethyl ether (DME) is generally constrained by the loss of Cu0 sites during the reaction. Previous studies have focused on introducing additional elements to improve the stability of active sites. In this study, an electron redistribution of the Cu/Cu2O interface was constructed. Surface Cu0 provides active sites for H2 adsorption and dissociation, and the Cu0/Cu+ interface sites are more beneficial for the activation and hydrogenation of CO2. The Ointer–H moieties that form at interface sites reduce the reaction energy barrier of CH3OH synthesis, and the decomposition of H2COOH* to CH2O* species is the rate-limiting step. In addition, the Cu0/Cu+ interface restricts the migration of copper species and protects the weak acid sites of HZSM-5 during the reaction. The present work provides an atomic-level description of H2 dissociation and CO2 activation by Cu0/Cu+ surface and interface sites.

Solvent-free selective hydrogenation of nitroaromatics to azoxy compounds over Co single atoms decorated on Nb2O5 nanomeshes

The solvent-free selective hydrogenation of nitroaromatics to azoxy compounds is highly important, yet challenging. Herein, we report an efficient strategy to construct individually dispersed Co atoms decorated on niobium pentaoxide nanomeshes with unique geometric and electronic properties. The use of this supported Co single atom catalysts in the selective hydrogenation of nitrobenzene to azoxybenzene results in high catalytic activity and selectivity, with 99% selectivity and 99% conversion within 0.5 h. Remarkably, it delivers an exceptionally high turnover frequency of 40377 h–1, which is amongst similar state-of-the-art catalysts. In addition, it demonstrates remarkable recyclability, reaction scalability, and wide substrate scope. Density functional theory calculations reveal that the catalytic activity and selectivity are significantly promoted by the unique electronic properties and strong electronic metal-support interaction in Co1/Nb2O5. The absence of precious metals, toxic solvents, and reagents makes this catalyst more appealing for synthesizing azoxy compounds from nitroaromatics. Our findings suggest the great potential of this strategy to access single atom catalysts with boosted activity and selectivity, thus offering blueprints for the design of nanomaterials for organocatalysis.

Molybdenum-doping promoted surface oxygen vacancy of CeO2 for enhanced low-temperature CO2 methanation over Ni-CeO2 catalysts

It is challenging to improve the low-temperature activity of Ni-based catalyst for the CO2 methanation reaction. In this study, a molybdenum-doped cerium oxide supported Ni catalyst (Ni/MoCe) was constructed, and it showed remarkable CO2 methanation performance at low temperatures (<300 °C). Structural analysis revealed that the incorporation of Mo into the CeO2 lattice could enrich the surface oxygen vacancies, reduce the particle size of Ni species and enhance the metal-support interaction. The Ni/MoCe demonstrated a faster HCOO* pathway for the conversion of CO2 to CH4 compared with Ni/CeO2. Besides, the rich surface oxygen vacancies in Ni/MoCe facilitated the adsorption form of bidentate carbonates and the enhanced Ni-CeO2 interaction reduced the approach resistance of active H species from Ni for subsequent hydrogenation process. This work proves that Mo doping is an effective vacancy engineering strategy to design high-performance heterogeneous catalysts for CO2 hydrogenation.

Rational Design and Precise Synthesis of Single-Atom Alloy Catalysts for the Selective Hydrogenation of Nitroarenes.

Single-atom alloys (SAAs) have gained increasing prominence in the field of selective hydrogenation reactions due to their uniform distribution of active sites and the unique host-guest metal interactions. Herein, 15 SAAs are constructed to comprehensively elucidate the relationship between host-guest metal interaction and catalytic performance in the selective hydrogenation of 4-nitrostyrene (4-NS) by density functional theory (DFT) calculations. The results demonstrate that the SAAs with strong host-guest metal interactions exhibit a preference for N─O bond cleavage, and the reaction energy barrier of the hydrogenation process is primarily influenced by the host metal. Among them, Ir1Ni SAA stands out as the prime catalyst candidate, showcasing exceptional activity and selectivity. Furthermore, the Ir1Ni SAA is subsequently prepared through precise synthesis techniques and evaluated in the selective hydrogenation of 4-NS to 4-aminostyrene (4-AS). As anticipated, the Ir1Ni SAA demonstrates extraordinary catalytic performance (yield>96%). In situ FT-IR experiments and DFT calculations further confirmed that the unique host-guest metal interaction at the Ir-Ni interface site of Ir1Ni SAA endows it with excellent 4-NS selective hydrogenation ability. This work provides valuable insights into enhancing the performance of SAAs catalysts in selective hydrogenation reactions by modulating the host-guest metal interactions.

Ru embedded into N-Doped Porous Carbon Nanosheets as a Robust Catalyst for Efficient Hydrogenation of Levulinic Acid to γ-Valerolactone

Ru embedded into N-Doped Porous Carbon Nanosheets as a Robust Catalyst for Efficient Hydrogenation of Levulinic Acid to γ-Valerolactone

Thermally stable Ni foam-supported inverse CeAlOx/Ni ensemble as an active structured catalyst for CO2 hydrogenation to methane

Nickel is the most widely used inexpensive active metal center of the heterogeneous catalysts for CO2 hydrogenation to methane. However, Ni-based catalysts suffer from severe deactivation in CO2 methanation reaction due to the irreversible sintering and coke deposition caused by the inevitable localized hotspots generated during the vigorously exothermic reaction. Herein, we demonstrate the inverse CeAlOx/Ni composite constructed on the Ni-foam structure support realizes remarkable CO2 methanation catalytic activity and stability in a wide operation temperature range from 240 to 600 °C. Significantly, CeAlOx/Ni/Ni-foam catalyst maintains its initial activity after seven drastic heating-cooling cycles from RT to 240 to 600 °C. Meanwhile, the structure catalyst also shows water resistance and long-term stability under reaction condition. The promising thermal stability and water-resistance of CeAlOx/Ni/Ni-foam originate from the excellent heat and mass transport efficiency which eliminates local hotspots and the formation of Ni-foam stabilized CeAlOx/Ni inverse composites which effectively anchored the active species and prevents carbon deposition from CH4 decomposition.

Selectivity control between reverse water-gas shift and fischer-tropsch synthesis in carbon-supported iron-based catalysts for CO2 hydrogenation

CO2 hydrogenation to chemicals and fuels has the potential to alleviate CO2 emissions and displace fossil resources simultaneously via consecutive RWGS and FTS reactions, also known as CO2-FTS. As Fe-based catalysts are active and selective for both reactions, their bifunctionality requires a delicate balance between the RWGS and FTS. In this work, we investigated the thermodynamic constraints of RWGS and CO2-FTS, the influence of CO2 conversion on selectivity and the influence of Fe nanoparticle size within the range of 4.7 to 10.3 nm. An inert carbon support was selected to rule out metal-support interaction and promoting effects of the support. Catalytic performance was evaluated at 300 °C, 11 bar, H2/CO2/Ar = 3/1/1, 600 to 72000 mL·gcat-1·h-1. At a CO2 conversion level below RWGS equilibrium conversion of 23 %, RWGS was found to be the primary and dominant reaction. No primary Sabatier reaction was observed. At higher CO2 conversion till the CO2-FTS threshold of 42 %, the secondary FTS reaction became dominant. Notably, a non-linear relation between CO2 conversion and CO selectivity was discovered. Comparing two catalysts with identical 5 wt% Fe loading but different average Fe nanoparticle size (6.6 and 8.4 nm), the 8.4 nm Fe catalyst was at least two times more active than the 6.6 nm Fe catalyst. In situ Mössbauer spectroscopy suggested a positive correlation between particle size, carburization and selectivity towards long-chain hydrocarbons. For these potassium-promoted carbon-supported Fe-based catalysts, nanoparticles of at least 8 nm are required for the formation of Fe carbides and improved reactivity.

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.

Titania-crystal-phase-engineered strong metal-support interactions and catalysis in CO2 hydrogenation

Tailoring strong metal-support interactions (SMSIs) have been verified to become an efficient strategy for developing novel heterogeneous catalysts. Here, both TiO2 supports (anatase (A) and rutile (R)) were employed to prepare the Pd/TiO2 catalysts and strongly titania-crystal-phase-dependent Pd-TiO2 SMSIs and catalysis in CO2 hydrogenation were observed. A-TiO2 is more facile to undergo Pd-TiO2 SMSIs than R-TiO2, which could be relevant to better reducibility over calcined Pd/A-TiO2C catalyst. Catalytic performance of the Pd/TiO2-R (reduced) catalysts in CO2 hydrogenation are sensitive to the Pd-TiO2 structures, among which the Pd nanoparticles mostly encapsulated by TiO2-x overlayers over Pd/A-TiO2-R catalyst with more prominent SMSIs is more intrinsically active. This could be ascribed to both stronger H-spillover and hydrogenation property and better CO2 activation capacity over Pd/A-TiO2-R catalyst. However, its catalytic activity is seriously restricted by the number of intrinsically active sites due to less exposed Pd atoms to block H2 activation sites. These results clearly demonstrate the crystal-phase engineering as an efficient strategy to tailor the SMSIs for developing improved heterogeneous catalysts.