Catalyst For Dehydrogenation Of Formic Acid Research Articles

Transition metal pincer catalysts for formic acid dehydrogenation: a mechanistic perspective.

The storage and transportation of hydrogen gas, a non-polluting alternative to carbon-based fuels, have always been challenging due to its extreme flammability. In this regard, formic acid (FA) is a promising liquid organic hydrogen carrier (LOHC), and over the past decades, significant progress has been made in dehydrogenating FA through transition metal catalysis. In this review, our goal is to provide a detailed insight into the existing processes to expose various mechanistic challenges associated with FA dehydrogenation (FAD). Specifically, methodologies catalyzed by pincer-ligated metal complexes were chosen. Pincer ligands are preferred as they provide structural rigidity to the complexes, making the isolation and analysis of reaction intermediates less challenging and consequently providing a better mechanistic understanding. In this perspective, the catalytic activity of the reported pincer complexes in FAD was overviewed, and more importantly, the catalytic cycles were examined in detail. Further attention was given to the structural modifications, role of additives, reaction medium, and their crucial effects on the outcome.

Ultrasmall Pd nanoparticles supported on a metal–organic framework DUT-67-PZDC for enhanced formic acid dehydrogenation

The highly dispersed ultrasmall palladium nanoparticles (Pd NPs) (1.7 nm) were successfully immobilized on a N-containing metal–organic framework (MOF, DUT-67-PZDC) using a co-reduction method, and it is used as an excellent catalyst for formic acid dehydrogenation (FAD). The optimized catalyst Pd/DUT-67-PZDC(10, 10 wt% Pd loading) shows 100% hydrogen (H2) selectivity and formic acid (FA) conversion at 60 °C, and the commendable initial turnover frequency (TOF) values of 2572 h−1 with the sodium formate (SF) as an additive and 1059 h−1 even without SF, which is better than most reported MOF supported Pd monometallic heterogeneous catalysts. The activation energy (Ea) of FAD is 43.2 KJ/mol, which is lower than most heterogeneous catalysts. In addition, the optimized catalyst Pd/DUT-67-PZDC(10) maintained good stability over five consecutive runs, demonstrating only minimal decline in catalytic activity. The outstanding catalytic performance could be ascribed to the synergistic corporations of the unique structure of DUT-67-PZDC carrier with hierarchical pore characteristic, the metal-support interaction (MSI) between the active Pd NPs and DUT-67-PZDC, the highly dispersed Pd NPs with ultrafine size serve as the catalytic active site, as well as the N sites on the support could act as the proton buffers. This work provides a new paradigm for the efficient H2 production of FAD by constructing highly active heterogeneous Pd-based catalysts using MOF supports.

Computational study on graphdiyne supported PdxCuy clusters as potential catalysts for formic acid dehydrogenation

Designing low-cost and efficient catalysts for formic acid dehydrogenation (FAD) is crucial to facilitate the practical applications of formic acid as a hydrogen carrier. Using density functional theory calculations, we designed nine graphdiyne-supported Pd/Cu single-, double-, and triple-atom catalysts, investigating their stability and formic acid dehydrogenation performance. The results indicate that as the number of active metal sites increases, the catalytic activity for formic acid dehydrogenation improves, i.e., M3@GDY > M2@GDY > M1@GDY (M = Pd/Cu). Moreover, a synergistic effect between Pd and Cu atoms is observed in PdxCu3-x@GDY, where the activity sequence of triple-atom catalysts was Pd1Cu2@GDY > Pd2Cu1@GDY > Pd3@GDY > Cu3@GDY. Particularly, Pd1Cu2@GDY exhibits superior FAD catalytic activity and hydrogen selectivity, presenting a potential novel formic acid dehydrogenation catalyst. Electronic structure analysis indicates that the band center difference Δε (Δε = εd - εp) serves as an assessment descriptor for formic acid dehydrogenation activity. Microkinetic analysis further confirms the performance of TACs predicted by DFT results, and shows that all TACs have good H2 selectivity even at a high temperature.

Boosting Effect of Sterically Protected Glucosyl Substituents in Formic Acid Dehydrogenation by Iridium(III) 2-Pyridineamidate Catalysts.

[Cp*Ir(R-pica)Cl] (Cp* = pentamethylcyclopentadienyl anion, pica = 2-picolineamide) complexes bearing carbohydrate substituents on the amide nitrogen atom (R = methyl-β-D-gluco-pyranosid-2-yl, 1; methyl-3,4,6-tri-O-acetyl-β-D-glucopyranosid-2-yl, 2) were tested as catalysts for formic acid dehydrogenation in water. TOFMAX values over 12000 h-1 and 50000 h-1 were achieved at 333 K for 1 and 2, respectively, with TON values over 35000 for both catalysts. Comparison with the simpler cyclohexyl-substituted analogue (3) indicated that glucosyl-based complexes are much better performing under the same experimental conditions (TOFMAX = 5144 h-1, TON = 5000 at pH 2.5 for 3) owing to a lower tendency to isomerize to the less active k2-N,O isomer upon protonation. The 5-fold increase in TOFMAX observed for 2 with respect to 1 is reasonably due to an optimal steric protection by the acetyl substituent, which may prevent unproductive inner-sphere reactivity. These results showcase a powerful strategy for the inhibition of the common deactivation pathways of [Cp*Ir(R-pica)X] catalysts for FA dehydrogenation, paving the way for the development of better performing hydrogen storage systems.

Efficient Atomically Dispersed Co/N-C Catalysts for Formic Acid Dehydrogenation and Transfer Hydrodeoxygenation of Vanillin.

Atomically dispersed catalysts have gained considerable attention due to their unique properties and high efficiency in various catalytic reactions. Herein, a series of Co/N-doped carbon (N-C) catalysts was prepared using a metal-lignin coordination strategy and employed in formic acid dehydrogenation (FAD) and hydrodeoxygenation (HDO) of vanillin. The atomically dispersed Co/N-C catalysts showed outstanding activity, acid resistance, and long-term stability in FAD. The improved activity and stability may be attributed to the high dispersion of Co species, increased surface area, and strong Co-N interactions. XPS and XAS characterization revealed the formation of Co-N3 centers, which are assumed to be the active sites. In addition, DFT calculations demonstrated that the adsorption of formic acid on single-atom Co was stronger than that on Co13 clusters, which may explain the high catalytic activity. The Co/N-C catalyst also showed promising performance in the transfer HDO of vanillin with formic acid, without any external additional molecular H2.

Exploring the Effects Behind the Outstanding Catalytic Performance of PdAg Catalysts Supported on Almond Shell‐Derived Activated Carbon Towards the Dehydrogenation of Formic Acid

AbstractIn this work, highly efficient carbon‐supported Pd‐based catalysts for formic acid dehydrogenation were synthesized by a straightforward wet impregnation‐reduction method. The carbon support was obtained from a biomass residue (almond shell) prepared via H3PO4‐assisted hydrothermal carbonization (HTC) and thermal activation. This carbon support was doped with nitrogen groups to study the effect on the electronic properties and catalytic performance of the catalysts. Investigating the formation of PdAg alloys with varying Pd : Ag molar ratios resulted in catalysts exhibiting enhanced catalytic activity compared to monometallic Pd counterparts. Notably, the Pd1Ag0.5/NAS catalyst displayed outstanding catalytic performance, achieving an initial TOF of 1716 h−1 (calculated in the first 3 minutes of reaction and expressed per mole of Pd) and maintaining substantial activity over 6 consecutive reaction cycles. This work elucidates the successful synthesis of effective catalysts, emphasizing the influence of nitrogen doping and PdAg alloy composition on catalytic behavior and stability.

Unveiling proton-responsive sites and reaction mechanisms in formic acid dehydrogenation catalyzed by Cp*Ir(III)-Pyridylpyrrole complexes: A DFT study

Transition metal catalysts based on proton-responsive ligands are crucial in the realm of chemical hydrogen storage. Nevertheless, the existence of multiple proton-responsive active sites on the ligand adds complexity to the mechanism, limiting our understanding of mechanistic preferences. In this study, density functional theory calculations are used to clarify the mechanistic preferences of iridium catalysts with multiple proton-responsive sites on the ligand for formic acid dehydrogenation. The calculated results show that, with the assistance of the α carbon atom (C2) of the pyrrole ligand site, the catalyst undergoes through an inner-sphere stepwise dehydrogenation mechanism. Moreover, the proton shuttle mechanism efficiently reduces the activation energy needed for H2 production, and solvent-assisted dehydrogenation shows lower energy barriers than substrate-assisted dehydrogenation. The reasons for mechanistic selectivity are further elucidated through Fukui function analysis, molecular plane parameter analysis, and the distortion-interaction model. These findings are anticipated to establish a theoretical foundation for the future design of high-performance catalysts for formic acid dehydrogenation.

Bimetallic PdAg clusters loaded on hierarchical self-pillared pentasil zeolite as efficient catalysts for formic acid dehydrogenation

In the present study, siliceous self-pillared pentasil (SPP) zeolite with regular mesopores was synthesized and used as a support for anchoring bimetallic PdAg clusters through a facile impregnation-reduction method. The as-prepared PdAg/SPP catalysts with different Pd/Ag ratios were demonstrated to catalyze formic acid dehydrogenation for hydrogen production. XRD results confirmed the formation of PdAg alloy on the surface of SPP zeolite. The Pd7Ag3/SPP catalyst showed high activity at 80 °C with an initial turn-over frequency (TOF) of 1263.6 h−1, proving the strategy using hierarchical SPP zeolite as carrier is advantageous over bulky zeolites for making highly active formic acid dehydrogenation catalysts.

Anchoring PdAg alloys on self-crosslinked carbon dots as efficient catalysts for formic acid dehydrogenation under ambient conditions

The optimized Pd0.9Ag0.1/CDs catalyst can catalyze complete dehydrogenation of FA in 9.5 min with a TOF value of 617 h−1 at 298 K. This work provides a simple approach for the fabrication of CDs supported highly distributed PdAg alloy catalysts.

Amine-functionalized Schiff base covalent organic frameworks supported PdAuIr nanoparticles as high-performance catalysts for formic acid dehydrogenation and hexavalent chromium reduction

Formic acid (FA) holds significant potential as a liquid hydrogen storage medium. However, it is important to improve the reaction rates and extend the practical applications of FA dehydrogenation and Cr(VI) reduction through the development of efficient heterogeneous catalysts. This study reports the synthesis of a uniformly dispersed PdAuIr nanoparticles (NPs) catalyst loaded with amine groups covalent organic frameworks (COFs). The alloyed NPs demonstrated exceptional effectiveness in FA dehydrogenation rate and Cr(VI) reduction. The initial turnover of frequency (TOF) value for FA dehydrogenation without additives was 9970 h−1 at 298 K, the apparent activation energy (Ea) was 30.3 kJ/mol and the rate constant (k) for Cr(VI) reduction was 0.742 min−1. Additionally, it showcased the ability to undergo recycling up to six times with minimal degradation in performance. The results indicate that its remarkable catalytic performance can be attributed primarily to the favorable mass transfer attributes of the aminated COFs supports, the strong metal-support interaction (SMSI), and the synergistic effects among the metals. This study offers a novel perspective on the advancement of efficient and durable heterogeneous catalysts with diverse capabilities, thereby making significant contributions to the fields of energy and environmental preservation.

Cellulose nanocrystals supported ternary alloy nanoclusters catalysts for efficient hydrogen production from formic acid

Formic acid has gained a lot of attention as one of the most promising liquid hydrogen storage carriers. Designing efficient and cost-effective heterogeneous catalysts for formic acid dehydrogenation can effectively address the challenges of in-situ hydrogen production, storage and transportation. In this study, the Au0.4Pd0.6Pt0.2 alloys with an ultrafine size (∼2nm) were prepared on amino-modified cellulose nanocrystals (CNC) with a total metal consumption of only 0.01mmol. The interaction between the support and nanoclusters provided the stable local environment for the catalysts, which showed remarkable HCOOH catalytic performance at low metal dosage, with TOFinitial of is 4478 h−1 and an Ea of 54.06kJ mol−1 at 323K, and the selectivity of hydrogen is 100%. Density functional theory (DFT) calculations demonstrated that the optimized local electron environment facilitated the OH bond cleavage and reduced the binding energy barrier between H*. This finding is beneficial to the development of more effective catalysts in the future.

Anchoring PdAu nanoclusters inside aminated metal-organic framework for fast dehydrogenation of formic acid

Liquid sunshine formic acid (FA), which is obtainable through CO2 hydrogenation with green H2 or biomass processing, is regarded as a prospective liquid organic hydrogen carrier (LOHC) owing to its high volumetric capacity (53 g H2 L−1), stability, and renewability. The search for effective catalysts to produce H2 from additive-free FA under ambient conditions is necessary but remains a challenge. Herein, highly dispersed and ultrafine PdAu nanoclusters (NCs) (1.2 nm) anchored by the aminated metal–organic framework (NH2-MIL-101) were successfully fabricated using a facile wet-chemical method and employed as a superior catalyst for formic acid dehydrogenation (FAD). The resulting PdAu/NH2-MIL-101 catalyst demonstrates 100 % H2 selectivity and superior performance with a turnover frequency value reaching 2921.0 h−1 at 323 K without any additive. Under similar conditions, this value is higher than the majority of published MOF-based FAD heterogeneous catalysts. The superior performance of PdAu/NH2-MIL-101 originates from a synergistic combination of the promoting effect of amino groups, the effective electronic coupling of Pd and Au, and the strong metal-support interaction between PdAu NCs and NH2-MIL-101, which promote the formation of reactive PdAu NCs and thus greatly improve catalytic performance. This work may provide important inspiration for developing highly efficient catalysts and strongly promote FA as a promising LOHC for chemical H2 storage.

Fast and Durable Dehydrogenation of Formic Acid over Pd–Cr(OH)3 Nanoclusters Immobilized on Amino-Modified Reduced Graphene Oxide

Formic acid, attractive as a renewable and safe liquid organic hydrogen carrier (LOHC), can be obtained by biomass conversion and CO2 hydrogenation with green hydrogen. The efficient and durable catalysts for formic acid dehydrogenation (FAD) are beneficial in the industry. Herein, Cr(OH)3-promoted Pd nanoclusters (NCs) (i.e., 1.6 nm) immobilized on amino-modified reduced graphene oxide (NH2-rGO) were successfully prepared through a simple wet-chemical approach. The obtained Pd–Cr(OH)3/NH2-rGO catalyst exhibits excellent catalytic activity and 100% hydrogen selectivity for CO-free FAD, giving a high turnover frequency of 2519.5 h–1 at 323 K, outperforming most reported Pd-based heterogeneous catalysts. Especially, the catalyst possesses robust durability toward FAD with no significant decline in activity and aggregation of metal NCs even after 10 cycles. The superior performance of the catalyst may be ascribed to the well-distributed Pd–Cr(OH)3 NCs, the strong electronic coupling of Pd with Cr(OH)3, the synergetic interaction of Pd–Cr(OH)3 with NH2-rGO, and the promotion effect of amino group. The reaction mechanism of FAD was explored based on the isotope experiments. This work provides insights into designing an effective and durable heterogeneous catalyst for dehydrogenation of LOHC.

Designing a Robust Palladium Catalyst for Formic Acid Dehydrogenation

Designing a Robust Palladium Catalyst for Formic Acid Dehydrogenation

A ligand design strategy to enhance catalyst stability for efficient formic acid dehydrogenation.

New Ir complexes bearing N-(methylsulfonyl)-2-pyridinecarboxamide (C1) and N-(phenylsulfonyl)-2-pyridinecarboxamide (C2) were employed as catalysts for aqueous formic acid dehydrogenation (FADH). The ligands were designed to maintain the picolinamide skeleton and introduce strong sigma sulfonamide moieties. C1 and C2 exhibited good stability towards air and concentrated formic acid (FA). During 20 continuous cycles, C1 and C2 could achieve the complete conversion of FA with TONs of 172 916 and 172 187, respectively. C1 achieved a high TOF of 19 500 h-1 at 90 °C and an air-stable Ir-H species was observed by 1H NMR spectroscopy.

A Low-Coordinate Iridium Complex with a Donor-Flexible O,N-Ligand for Highly Efficient Formic Acid Dehydrogenation

Formic acid is one of the most promising hydrogen carriers. Here, we report on a highly productive iridium-based catalyst for formic acid dehydrogenation, which is based on an underligated iridium(III) center containing a donor-flexible pyridylidene-amine ligand containing a chelating phenolate. This complex reaches temperature-dependent turnover frequencies from 2000 (40 °C) to 280000 h–1 (100 °C) and up to 3 million turnover numbers, thus outperforming state-of-the-art systems. The high efficiency together with the remarkably low cost and easy accessibility of the complex (<$100/g) are attractive features for industrial applications.

Hydrogen generation over Ni@Pd NCs through an active H-exchange from formic acid-water system

The use of Formic acid as an alternative to fossil fuels is promising, both from economical and ecological standpoints, and has received great of attention owing to its inherently superiority in recent decades. Nevertheless, efficient and low-cost solid catalyst for formic acid dehydrogenation at room temperature still constitutes a biggish challenge. Moreover, comparing to increase the catalytic performance of catalysts, very little attention payed to the kinetic mechanism of dehydrogenation reaction because of the lack of effective characterization artifice. Here, the as-prepared Ni@Pd nanoparticles by a sequential reduction process can be useful catalyst for formic acid decomposition at room temperature without a promoter. Thanks to the effective catalyst and isotope distribution technique, preliminary mechanistic results firstly reveal that hydrogen is obtained via a H-atom recombination on isolated sites after the proton exchange randomly between activated H and solvent.

Dehydrogenation of formic acid mediated by a Phosphorus–Nitrogen PN3P-manganese pincer complex: Catalytic performance and mechanistic insights

The utilization of formic acid as a liquid organic hydrogen carrier has taken a vast interest lately because of several desirable properties. The state-of-the-art homogenous catalysts known for formic acid dehydrogenation are mainly based on noble metals such as iridium or ruthenium. 3d metals are considered to be an attractive alternative due to their abundance and low toxicity. Exploration of 3d metals has achieved exciting results mainly with iron-based catalysts; however, manganese has not received much attention, and only a few examples are available. Here we report a manganese complex [Mn(PN3P)(CO)2]Br containing a pincer backbone, as an efficient catalyst for formic acid dehydrogenation. Under the optimized condition, the complex afforded a TON of 15,200. To the best of our knowledge, this is considered one of the best TON achieved using a manganese-based complex with excellent selectivity. Mechanistic studies suggested that the imine arm participates in the formic acid activation/deprotonation step, emphasizing the importance of metal-ligand cooperativity during substrate activation to promote catalytic efficacy.

Defect-dominated carbon deposited Pd nanoparticles enhanced catalytic performance of formic acid dehydrogenation

The defect-rich characteristic nanostructure carbon favors the changing polarity and electron distribution in carbon matrix, thus facilitating an efficient adsorption of ions. Herein, a B,N,F-tridoped carbon material is successfully prepared on defect-rich sites by directly calcining two sodium salts, namely ethylenediaminetetraacetic acid tetrasodium salt (Na4EDTA) and ammonium tetrafluoroborate (NH4BF4). B refers to electron-donating atoms while F and N are electron-accepting atoms. The co-existence of electron-donating and electron-accepting atoms causes an asymmetrical spin and charge density, favoring palladium nanoparticles (Pd NPs) well dispersed on the carbon matrix. The heteroatoms efficiently control over the growth of Pd NPs and regulate the internal electron density. The catalytic performance is significantly enhanced with the obtained Pd/BNF-C catalyst for formic acid dehydrogenation, which has a lower activation barrier (36.4 kJ/mol) and a better reusability than those of free-heteroatom catalysts. The efficiency might be attributed to the strong interaction between Pd NPs and heteroatoms, and the electrons transfer from carbon material to Pd NPs, with benefits including the significant coupling effect of B,N,F-tridoping down to the atomic scale, abundant surface active defects, in-plane nanopore defects and more adjacent metal active sites.

Study of Non-Noble-Metal-Based Metal–Nitrogen–Carbon Catalysts for Formic Acid Dehydrogenation

Study of Non-Noble-Metal-Based Metal–Nitrogen–Carbon Catalysts for Formic Acid Dehydrogenation