Catalysts For Hydrogenation Research Articles

Active Sites of Cu/ZnO-Based Catalysts for CO2 Hydrogenation to Methanol: Part III

Part II of this review examines how preparation methods influence catalyst performance and the impact of doping with elements like ceria, alumina and zirconia on CO2 conversion selectivity. We conclude that zinc oxide enhances copper dispersion and promotes a synergistic effect at the interface, leading to improved catalytic performance. This work presents the continuation of and conclusions from Parts I () and II ().

Ag nanoparticles on arginine-cyanoguanidine functionalized magnetic g-C3N4: A catalyst for nitroaromatic hydrogenation and regioselective click reactions

This study describes the development of a novel hybrid nanocatalyst that was obtained by doping magnetic g-C3N4 with Ag nanoparticles and modifying it with arginine and cyanoguanidine (Ag@Fe3O4-g-C3N4-Arg-CG). Comprehensive characterization of the nanocatalyst using techniques such as FTIR, XRD, SEM, and TGA confirmed its structural and morphological properties. The catalytic efficiency of the synthesized nanostructure was evaluated in two key reactions: the reduction of nitroaromatic compounds and a click reaction for 1,2,3-triazole synthesis. The results demonstrate that Ag@Fe3O4-g-C3N4-Arg-CG effectively reduced various nitroaromatic compounds to substituted anilines at room temperature using NaBH4 as the reducing agent. Nitrobenzene reduction did not proceed in aprotic solvents such as acetonitrile, CH2Cl2, and dimethylformamide, whereas it exhibited a high reaction yield in protic solvents such as ethanol and water. The highest yield (100 %) was observed in water at 50 °C using H2O solvent. Additionally, the nanohybrid exhibited significant potential for “green” click chemistry by efficiently synthesizing 1,2,3-triazoles under mild conditions, with low catalyst loading. Its magnetic properties facilitated easy recovery, and the catalyst maintained high activity over six cycles, making it suitable for sustainable applications in organic transformations.

Active Sites of Cu/ZnO-Based Catalysts for CO2 Hydrogenation to Methanol: Part II

Part II of this review continues to explore the connection between Cu/ZnO-based catalysts properties and methanol synthesis activity. This work continues from Part I ().

Synergistic effect of carbon molecular sieve and alkali metal nitrate on promoting intermediate-temperature adsorption of CO2 over MgAl-layered double hydroxide

The development of intermediate-temperature adsorbents with high CO2 adsorption capacity is crucial for the tandem integration with CO2 hydrogenation catalyst, aimed at enhancing economy viability and minimizing energy consumption in Carbon capture, utilization and storage (CCUS). Although certain porous carbon materials (PCM) have been employed to enhance CO2 adsorption capability of layered double hydroxide (LDH), there remains an urgent necessity to identify more cost-effective and efficient PCM alternatives. Herein, alkali metal nitrates ((Li0.3Na0.18K0.52)NO3, hereafter referred to as LiNaK) modified layered double hydroxide (LDH)/carbon molecular sieve (CMS) composite (LiNaK-LDH/CMS) as promising adsorbents for CO2 capture was reported. The effects of CMS addition and nitrate loading, the calcination and adsorption temperature, as well as the cycling stability were investigated systematically. The results revealed that the CO2 capture capacity of the LiNaK-modified layered double oxide (LDO)/CMS composite (30 mol%LiNaK-LDO/CMS15%)-incorporating with 15 wt% CMS addition and 30 mol% nitrate loading-achieved a remarkable CO2 adsorption capacity of 1.32 mmol/g at 300 °C due to the synergetic interactions between CMS and nitrate; this represents nearly a sevenfold enhancement compared to initial LDO performance. Moreover, the 30 mol%LiNaK-LDO/CMS15% adsorbent also demonstrated commendable cyclic stability after ten adsorption cycles, retaining over 85 % of its initial adsorption capacity. Based on both obtained adsorption performance and characterization data from the adsorbents, a pre-adsorption enhancing CO2 intermediate-temperature adsorption mechanism over LiNaK-LDH/CMS composite through air calcination processes. This study significantly advances LDH-based adsorbent for future research into CO2 intermediate-temperature adsorption.

Carbon-Supported Fe-Based Catalyst for Thermal-Catalytic CO2 Hydrogenation into C2+ Alcohols: The Effect of Carbon Support Porosity on Catalytic Performance

Carbon materials supported Fe-based catalysts possess great potential for the thermal-catalytic hydrogenation of CO2 into valuable chemicals, such as alkenes and oxygenates, due to the excellent active sites’ accessibility, appropriate interaction between the active site and carbon support, as well as the excellent capacities in C-O bond activation and C-C bond coupling. Even though tremendous progress has been made to boost the CO2 hydrogenation performance of carbon-supported Fe-based catalysts, e.g., additives modification, the choice of different carbon materials (graphene or carbon nanotubes), electronic property tailoring, etc., the effect of carbon support porosity on the evolution of Fe-based active sites and the corresponding catalytic performance has been rarely investigated. Herein, a series of porous carbon samples with different porosities are obtained by the K2CO3 activation of petroleum pitch under different temperatures. Fe-based active sites and the alkali promoter Na are anchored on the porous carbon to study the effect of carbon support porosity on the physicochemical properties of Fe-based active sites and CO2 hydrogenation performance. Multiple characterizations clarify that the bigger meso/macro-pores in the carbon support are beneficial for the formation of the Fe5C2 crystal phase for C-C bond coupling, therefore boosting the synthesis of C2+ chemicals, especially C2+ alcohols (C2+OH), while the limited micro-pores are unfavorable for C2+ chemicals synthesis owing to the sluggish crystal phase evolution and reactants’ inaccessibility. We wish our work could enrich the horizon for the rational design of highly efficient carbon-supported Fe-based catalysts.

Chiral Polymeric Diamine Ligands for Iridium-Catalyzed Asymmetric Transfer Hydrogenation.

A series of polymeric chiral diamine ligands are developed by diboron-templated asymmetric reductive couplings, and their iridium complexes Ir-polydiamines are efficient and recyclable catalysts for asymmetric transfer hydrogenation (ATH) of functionalized ketones, affording a series of optically active secondary alcohols in excellent enantioselectivities (up to 99% ee) and unprecedentedly high total TONs (12,000, six cycles). Ir-polydiamine catalysts with longer chains offered higher reactivities, providing a plausible deactivation mechanism and practical solutions of ATH for vitamin B5 and phenylephrine.

Bench-Stable Low-Valent Chromium Catalysts for Hydrogenation of CO2, Bicarbonate, and Inorganic Carbonates to Formate

Bench-Stable Low-Valent Chromium Catalysts for Hydrogenation of CO₂, Bicarbonate, and Inorganic Carbonates to Formate

Nanostructure of Indium-driven nickel catalysts break CO2 hydrogenation preference

Identifying the key factors governing the selectivity of CO2 hydrogenation catalysts remains a formidable challenge. Herein, we elucidate the complex interaction between active sites nanostructure and selectivity in CO2 hydrogenation through in-depth characterization and theoretical simulations. NiIn alloy formed on the Ni facets with hydrogen reduction, constructing a core-shell-like structure. Ni-mediated methane formation was suppressed almost entirely upon alloying with indium, allowing the reaction pathway shifted from methanation into the reverse-water-gas-shift (RWGS). On the contact surface, In restricted CO adsorption on Ni, thereby preventing methane generation from CO via successive hydrogenation. DFT calculations confirmed that Ni and CO are negatively charged and repel each other due to electron transfer from indium, resulting in a decrease in adsorption energy, which is crucial for the pathway shift. Understanding the regulation of Ni-In structure in product distribution is expect to provide valuable insights into the precise design of catalysts with controllable product selectivity.

Design and Understanding of Adaptive Hydrogenation Catalysts Triggered by the H2/CO2-Formic Acid Equilibrium.

An adaptive catalytic system for selective hydrogenation was developed exploiting the H2+CO2HCOOH equilibrium for reversible, rapid, and robust on/off switch of the ketone hydrogenation activity of ruthenium nanoparticles (Ru NPs). The catalyst design was based on mechanistic studies and DFT calculations demonstrating that adsorption of formic acid to Ru NPs on silica results in surface formate species that prevent C═O hydrogenation. Ru NPs were immobilized on readily accessible silica supports modified with guanidinium-based ionic liquid phases (Ru@SILPGB) to generate in situ sufficient amounts of HCOOH when CO2 was introduced into the H2 feed gas for switching off ketone hydrogenation while maintaining the activity for hydrogenation of olefinic and aromatic C═C bonds. Upon shutting down the CO2 supply, the C═O hydrogenation activity was restored in real time due to the rapid decarboxylation of the surface formate species without the need for any changes in the reaction conditions. Thus, the newly developed Ru@SILPGB catalysts allow controlled and alternating production of either saturated alcohols or ketones from unsaturated substrates depending on the use of H2 or H2/CO2 as feed gas. The major prerequisite for design of adaptive catalytic systems based on CO2 as trigger is the ability to shift the H2+CO2HCOOH equilibrium sufficiently to exploit competing adsorption of surface formate and targeted functional groups. Thus, the concept can be expected to be more generally applicable beyond ruthenium as the active metal, paving the way for next-generation adaptive catalytic systems in hydrogenation reactions more broadly.

Heteroatoms‐Stabilized Single Palladium Atoms on Amorphous Zeolites: Breaking the Tradeoff between Catalytic Activity and Selectivity for Alkyne Semihydrogenation

AbstractAs a fundamental industrial catalytic process, the semihydrogenation of alkynes presents a challenge in striking a balance between activity and selectivity due to the issue of over‐hydrogenation. Herein, we develop an efficient catalytic system based on single‐atom Pd catalysts supported on boron‐containing amorphous zeolites (Pd/AZ−B), achieving the tradeoff breaking between the activity and selectivity for the selective hydrogenation of alkynes. Advanced characterizations and theoretical density functional theory calculations confirm that the incorporated B atoms in the Pd/AZ−B can not only alter the geometric and electronic properties of Pd atoms by controlling the electron migration from Pd but also mitigate the interaction between alkene and the catalyst supports. This boosts the exceptional catalytic efficacy in the semihydrogenation of phenylacetylene to styrene under mild conditions (298 K, 2 bar H2), achieving a recorded turnover frequency (TOF) value of 24198 h−1 and demonstrating 95 % selectivity to styrene at full conversion of phenylacetylene. By comparison, the heteroatom‐free amorphous zeolite‐anchored Pd nanoparticles and the commercial Lindlar catalyst have styrene selectivities of 73 % and 15 %, respectively, under identical reaction conditions. This work establishes a solid foundation for developing highly active and selective hydrogenation catalysts by controllably optimizing their electronic and steric properties.

Heteroatoms-Stabilized Single Palladium Atoms on Amorphous Zeolites: Breaking the Tradeoff between Catalytic Activity and Selectivity for Alkyne Semihydrogenation.

As a fundamental industrial catalytic process, the semihydrogenation of alkynes presents a challenge in striking a balance between activity and selectivity due to the issue of over-hydrogenation. Herein, we develop an efficient catalytic system based on single-atom Pd catalysts supported on boron-containing amorphous zeolites (Pd/AZ-B), achieving the tradeoff breaking between the activity and selectivity for the selective hydrogenation of alkynes. Advanced characterizations and theoretical density functional theory calculations confirm that the incorporated B atoms in the Pd/AZ-B can not only alter the geometric and electronic properties of Pd atoms by controlling the electron migration from Pd but also mitigate the interaction between alkene and the catalyst supports. This boosts the exceptional catalytic efficacy in the semihydrogenation of phenylacetylene to styrene under mild conditions (298 K, 2 bar H2), achieving a recorded turnover frequency (TOF) value of 24198 h-1 and demonstrating 95 % selectivity to styrene at full conversion of phenylacetylene. By comparison, the heteroatom-free amorphous zeolite-anchored Pd nanoparticles and the commercial Lindlar catalyst have styrene selectivities of 73 % and 15 %, respectively, under identical reaction conditions. This work establishes a solid foundation for developing highly active and selective hydrogenation catalysts by controllably optimizing their electronic and steric properties.

A Selective Iron(I) Hydrogenation Catalyst.

Iron is the most abundant transition metal of the Earth's crust, and the understanding of its function in key technologies, such as catalysis, is highly important. We report here on an iron(I) hydrogenation catalyst. Our catalyst activates hydrogen via heterolytic bond cleavage, forms a monohydride, and hydrogenates polar double bonds via a bimetallic pathway (potassium-assisted hydride transfer). The mechanism observed seems to exclude oxidative addition and reductive elimination pathways, permitting the tolerance of numerous hydrogenation-sensitive functional groups, as demonstrated for the hydrogenation of C═O bonds.

Atomically Dispersed Palladium Catalyst for Chemoselective Hydrogenation of Quinolines.

Chemoselective hydrogenation of quinoline and its derivatives is a significant strategy to achieve the corresponding 1,2,3,4-tetrahydroquinolines (py-THQ) for various potential applications. Here, we precisely constructed a titanium carbide supported atomically dispersed Pd catalyst (PdSA+NC/TiC) for quinoline hydrogenation, delivering above 99% py-THQ selectivity at complete conversion with an outstanding turnover frequency (TOF) of 463 h-1. AC-HAADF-STEM and XAFS demonstrate that the atomic dispersion of Pd includes Pd-Ti2C2 single atoms and Pd clusters with atomic-layer thickness. Theoretical calculation and experimental results revealed that H2 dissociation and subsequent hydrogenation rates were greatly promoted over Pd clusters. Although the adsorption of quinolines and intermediates are easier on Pd clusters than on Pd single atoms, the desorption of py-THQ is more favored over Pd single atoms than over Pd clusters. The desorption step may be the main reason for 5,6,7,8-tetrahydroquinoline (bz-THQ) and decahydroquinoline (DHQ) formation. Thus, a low reaction activity and py-THQ selectivity were received over PdSA/TiC and PdNP/TiC, respectively.

CO2 hydrogenation to light olefins over highly active and selective Ga-Zr/SAPO-34 bifunctional catalyst

The production of light olefins from the hydrogenation of CO2 is an efficient way to utilize CO2, where the surface oxygen vacancy in metal oxide plays an important role in CO2 adsorption and activation. Here, the Ga-Zr metal oxides were prepared by hydrolysis of urea at different temperatures and combined with SAPO-34 to prepare the bifunctional catalyst for CO2 hydrogenation to light olefins. The surface oxygen vacancy content of Ga-Zr oxide increases with increasing urea hydrolysis temperature, and a high CO2 conversion of 26.4% and C2=–C4= hydrocarbon selectivity of 87.2% were obtained by a well-matched amount of desorbed CO2 and H2. Using the CO2 and H2/HCOOH/CH3OH as probe molecules, the in-situ DRIFT spectra reveal that the CO2 could be activated on surface oxygen vacancy and converted to CO3* and HCO3* species, which were further hydrogenated to HCOO* and CH3O* species. While the by-product CO mainly originates from the decomposition of HCOO* and the presence of SAPO-34 converts CH3O* to C2=–C4=. The current study illustrates that boosting the surface oxygen vacancy in defected surfaces of metal oxide and providing a matching H2 dissociation ability is the key to improve the performance of CO2 hydrogenation to light olefins.

Fine regulation of Cu-ZnO interfaces for enhanced CO2 hydrogenation to methanol by atomic layer depositing thin ZnO films on copper phyllosilicates

Regulation of abundant Cu-ZnO interfaces in Cu/ZnO catalysts is critical to the thermal hydrogenation of CO2 to methanol. Herein, Cu-ZnO interfaces were precisely regulated by depositing thin ZnO films on copper phyllosilicates (CuSiO3) through atomic layer deposition (ALD) to prepare Cu/ZnO/SiO2 composite catalysts (denoted as xZnO/CuSiO3, x is the number of ALD cycles) for CO2 hydrogenation to methanol. Interestingly, 5ZnO/CuSiO3 exhibited much higher methanol selectivity of 68.1 % and methanol space-time yield (STYMeOH) of 0.39 gMeOH h−1gcat−1 toward CO2 hydrogenation at 275 ℃ and 3 MPa, as compared to the pristine CuSiO3 (38.1 % and 0.24 gMeOH h−1gcat−1), suggesting the significant role of Cu-ZnO interfaces. Compared to ZnO/CuSiO3(IM) prepared by the conventional impregnation method, 5ZnO/CuSiO3 possessed much higher CO2 conversion (13.8 % vs. 10.1 %) and methanol selectivity (68.1 % vs. 56.2 %). Furthermore, the catalytic activities of the prepared Cu/ZnO catalysts can be effectively regulated by changing the thickness of ZnO-ALD films, in which 5ZnO/CuSiO3 showed the best catalytic activity. Various characterization methods were applied to demonstrate that ALD-ZnO was evenly laid flat on the surface of CuSiO3 to construct abundant Cu-ZnO interfaces during the H2 reduction treatment, which facilitated the dissociated activation of CO2 and formation of CH3O* reaction intermediate and simultaneously inhibited the generation of CO byproduct. In addition, the density functional theory (DFT) calculations revealed the stronger interaction between Cu and ZnO over 5ZnO/CuSiO3, which implied more Cu-ZnO interfaces were generated for methanol production. Accordingly, this study verifies the significance of Cu-ZnO interfaces for CO2 hydrogenation to methanol and provides a facile method to regulate Cu-ZnO interfaces by depositing ALD-ZnO films on the copper phyllosilicate precursor.

Selective reductive conversion of CO2 to CH2-bridged compounds by using a Fe-functionalized graphene oxide-based catalyst

Anthropogenic climate change drastically affects our planet, with CO2 being the most critical gaseous driver. Despite the existing carbon dioxide capture and transformation, there is much need for innovative carbon dioxide hydrogenation catalysts with excellent selectivity. Here, we present a fast, effective, and sustainable route for coupling diverse alcohols, amines and amides with CO2 via heterogenization of a natural metal-based homogeneous catalyst through decorating on functionalized graphene oxide (GO). Combined synthetic, experimental, and theoretical studies unravel mechanistic routes to convergent 4‑electron reduction of CO2 under mild conditions. We successfully replace the toxic and expensive ruthenium species with inexpensive, ubiquitously available and recyclable iron. This iron-based functionalized graphene oxide (denoted as Fe@GO-EDA, where EDA represents ethylenediamine) functions as an efficient catalyst for the selective conversion of CO2 into a formaldehyde oxidation level, thus opening the door for interesting molecular structures using CO2 as a C1 source. Overall, this work describes an intriguing heterogeneous platform for the selective synthesis of valuable methylene-bridged compounds via 4‑electron reduction of CO2.

Pd-imidate@SBA-15: a multifunctional heterogeneous catalyst for the aqueous room temperature hydrogenation of CO2 to formic acid.

The incorporation of hydrophilic and basic sites from phosphotriazaadamantane and saccharine in a water-soluble Pd complex and the subsequent confinement into mesoporous silica support increases the activity and stability of the palladium catalytic species for the room-temperature aqueous hydrogenation of either bicarbonate or CO2 into formic acid. The use of low Pd loadings (<0.1mmolPd·g-1) of the well-dispersed complex on SBA-15 mesoporous silica allows performing the reaction under room temperature, and aqueous conditions, exhibiting TON of ca. 40-100, for the CO2 or bicarbonate hydrogenation, respectively, which is one order of magnitude higher than the homogeneous case, allowing the easy isolation and recycling of the solid catalyst.

Integrating Multiple Strategies Using Biotechnology to Design High‐Performance Electrocatalysts for Hydrogen and Oxygen Evolution

AbstractCombining multiple design strategies often enhances catalyst performance but usually comes with high costs and low reproducibility. A technique that enhances catalyst performance in multiple strategies is urgently needed. Herein, a novel bioregulation technique is introduced, allowing simultaneous control over morphology, particle size, doping, interface engineering, and electronic properties. Bioregulation technique utilizes the soluble extracellular polymer from Aspergillus niger as a templating agent to construct high‐performance catalysts for hydrogen and oxygen evolution reaction (HER and OER). This technique controls catalyst morphology, introduces biological N and S doping, and regulates the electronic structure of the catalyst surface. Biomolecule modification enhances surface hydrophilicity, and the nanostructure increases surface roughness and gas‐release efficiency. Theoretical calculations show that the bioregulation technique shortens the d/p‐band center, optimizing reaction intermediate adsorption and desorption. The Bio‐Pt/Co3O4 catalyst with trace Pt on the surface, designed with these strategies, achieves HER (η10 of 42 mV), OER (η10 of 221 mV), and overall water‐splitting performance (1.51 V at 10 mA cm−2), maintaining stability for over 50 h, outperforming most Pt‐based catalysts. Notably, using spent lithium‐ion battery cathodes leachate, rich in Co2⁺, successfully replicates the experiment. This approach holds promise as a mainstream method for synthesizing high‐performance materials in the future.

Electrochemical Hydrogenation of N‐Heterocycles and Related Substrates: A Mini‐Review

ABSTRACTCatalytic hydrogenation refers to the (often) metal‐mediated addition of dihydrogen (H2) equivalents to unsaturated compounds to form new element‐hydrogen bonds. This conceptually simple reaction is ubiquitous in the production of a vast number of essential chemicals. Despite a growing recognition of the importance of sustainability in manufacturing, the use of fossil‐derived hydrogen gas and precious metal catalysts in hydrogenation remains widespread. Electrochemical variants of these processes are an appealing alternative, especially those that can make use of sustainable Brønsted acids, more abundant electrode materials and renewable electricity. In this mini‐review, we give a selective overview of electrochemical hydrogenation methodologies for N‐heterocycles and some related substrates from the specific perspective of the synthetic chemistry made possible by this increasingly popular approach.

Properties of PdAg/Al2O3 Egg–Shell Single-Atom Catalysts in Front-End Hydrogenation of Acetylene

Properties of PdAg/Al2O3 Egg–Shell Single-Atom Catalysts in Front-End Hydrogenation of Acetylene