Dehydrogenation Of Formic Acid Research Articles

Modified cellulose nanocrystals immobilized AuPd nanoalloy for formic acid dehydrogenation

Formic acid (FA) is regarded as a promising liquid organic hydrogen transporter. Herein, carriers for immobilizing ultrafine AuPd nanoparticles with a size of approximately 2 nm were produced using cellulose nanocrystals (CNCs) treated with polydopamine (PDA) and polyethyleneimine (PEI). Even with a low noble metal loading (0.01 mmol), the optimized Au0.4Pd0.6/PEI-PDA@CNCs demonstrated extremely high FA dehydrogenation activity compared with similar products, with 100% hydrogen selectivity and TOFinitial up to 4258 h−1 at 323 K. The modified CNCs can enhance the electron transfer between metal particles, and their optimization of the local electronic structure can improve the adsorption of the key intermediates of the reaction. The density functional theory (DFT) calculations were discovered the optimized local electron environment promotes bi-HCOO* rearrangement and lowers the energy barrier for H* and H* binding. This discovery can be used to develop more effective catalysts in the future.

Catalytic formic acid dehydrogenation via hexagonal-boron nitride supported palladium

Formic acid dehydrogenation is an effective pathway for hydrogen storage, transportation, and in situ supply; however, the problems of catalyst sintering and agglomeration remain challenging. In this regard, this study aims at modulating hexagonal boron nitride-supported Pd catalyst with strong metal support interactions, thereby promoting its long-term stability. Effects of particle sizes of h-BN (500 nm, 1–2 μm, 5–10 μm) and dehydrogenation temperatures on formic acid conversion, hydrogen yield, CO concentration, and product distribution are investigated. The nano-scaled h-BN supported Pd nanoparticles show the best performance of 24.25 mmol H2 mL-1 HCOOH with a H2 concentration of 44.7 vol%. Characterizations such as N2 adsorption and desorption, XRD, TEM-EDX mapping, and XPS are used to study the physicochemical properties of the as-synthesized and reacted catalysts. Specifically, the diffraction peaks of Pd cannot be detected from XRD, possibly attributing to the homogeneous dispersion of its nanoparticles, as confirmed by the TEM-EDX mapping results. The durability tests indicate that the Pd/h-BN (500 nm) catalyst remains long-term stability under a temperature as high as 160 °C. Moreover, results from XPS reveal that there is a strong interaction between the Pd nanoparticles and the hexagonal BN support, as proved by the electronic transformation from Pd to N by XPS, thereby enhancing the stability of the Pd/h-BN catalyst.

Ultra-small PdAuIr nanoparticles on amine-functionalized porous organic polymers for efficient dehydrogenation from FA at room temperature

Formic acid (FA) is a prospective hydrogen storage agent, which has attracted much attention for its low toxicity and stability and plays a significant role in the comprehensive implementation of the hydrogen economy. In this regard, it is very important to utilize additive free FA dehydrogenation, for which few heterogeneous catalysts are available. Herein, we report ultra-small PdAuIr nanoparticles (NPs) supported on amine-based amorphous porous organic polymers (POPs), which exhibit excellent FA dehydrogenation activity with an initial total turnover number (TOF) of 9635 h−1 without additives at room temperature and apparent activation energy (Eaapp) of 36.5 kJ/mol. The results show that the excellent performance can be attributed to the synergistic effect of trimetallic alloys and strong metal-support interaction effect (SMSI), as well as to the amine groups (-NH2) grafted on POPs which facilitates the O–H bond splitting on FA. Overall, the simple and efficient synthetic strategy provides a new method for the selective dehydrogenation of FA.

Elucidating the alloying effect of PdAg/CNT catalysts on formic acid dehydrogenation with kinetic isotope effect

Formic acid has emerged as a promising liquid hydrogen carrier for addressing the transport and storage issues of hydrogen, owing to its high hydrogen density (4.4 wt.%) and easy-handling liquid phase. Therefore, the conversion of formic acid into hydrogen and vice versa is a significant technique. Despite the development of various metal alloy catalysts for efficient production of hydrogen from formic acid, it remains unclear how the metal alloy affects formic acid dehydrogenation from the mechanistic perspective. This study addresses this gap by investigating the alloy effect of Pd and Ag on formic acid dehydrogenation, using PdAg alloy nanoparticles supported on carbon nanotube catalysts. The PdAg alloy, analyzed using multiple characterization methods, demonstrated enhanced catalytic activity, which was maximized at a Pd:Ag molar ratio of 7:3. More importantly, temperature-dependent and kinetic isotope effect experiments demonstrated that the electronic modification of Pd by Ag improved its activity by promoting the cleavage of the CH bond of formic acid. The results suggest that the kinetic isotope effect would be a potent technique for elucidating the alloying effect, as well as providing a deeper understanding of the mechanism.

New 3D Printing Strategy for Structured Carbon Devices Fabrication

This work shows a new method for the preparation of 100% carbon-structured devices. The method is based on resorcinol-formaldehyde polymerization, using starch as a binder with the addition of a certain amount of external carbon source before polymerization. Molds obtained by 3D printing are used to shape the structured devices in the desired shape, and the ultimate pyrolysis step consolidates and produces the carbonaceous devices. The proposed method allows obtaining supports with different textural and surface properties varying the carbonaceous source, the solvent, or the pyrolysis conditions, among other factors. The as-obtained devices have demonstrated their usefulness as palladium supports for the gas-phase formic acid dehydrogenation reaction. The monolith shows a high conversion of formic acid (81% according to H2 production) and a high selectivity towards hydrogen production at mild temperatures (80% at 423 K).

Formic Acid Dehydrogenation over a Monometallic Pd and Bimetallic Pd:Co Catalyst Supported on Activated Carbon

In this study, palladium is proposed as an active site for formic acid dehydrogenation reaction. Pd activity was modulated with Co metal with the final aim of finding a synergistic effect that makes possible efficient hydrogen production for a low noble metal content. For the monometallic catalysts, the metal loadings were optimized, and the increase in the reaction temperature and presence of additives were carefully considered. The present study aimed, to a great extent, to enlighten the possible routes for decreasing noble metal loading in view of the better sustainability of hydrogen production from liquid organic carrier molecules, such as formic acid.

Hydrogen-bonded network in interfacial water confer the catalysts with high formic acid decomposition performance

The importance of the dynamic structural evolution of water in the solid–liquid interface cannot be overstated. However, the ubiquitous hydrogen-bonded network is notoriously difficult to probe owing to complex interfacial environment. Formic acid, a fair hydrogen-bond donor and acceptor, is a promising reversible hydrogen storage/release material. Herein, isotope-labeled in-situ mass spectrometry (MS) and operando surface-enhanced Fourier transform infrared measurements (operando FT-IR) reveal the central role of water during formic acid dehydrogenation. The water-promoted restructured HCOONa-Pd@ANI/C catalyst exhibits 100% selectivity, 100% conversion yield with high stability (even after 112 days) under ambient conditions. Coupled to a proton exchange membrane fuel cell, this integrated system reaches a high power density at 29.81 W⋅gPd−1. Our study demonstrates a new pathway involving water, the indispensable proton transfer and exchange through efficiently hydrogen-bonded network in light of operando experimental evidence.

Synthesis of Ir Catalysts Featuring Amide‐functionalized NHC Ligands and Survey of their Activity on Formic Acid Dehydrogenation

Abstract2 a and 2 b, [Ir(CI)(COD)(NHC)] (COD=1,5‐cyclooctadiene), have been prepared via transmetallation from NHC−Ag complexes. [Rh(CI)(COD)(NHC)] (4) was prepared analogously. [Ir({κ‐C,N‐(NHC‐acetamide−1H)}(COD)] (3 c) has been synthesized via transmetallation from the deprotonated NHC−Ag complex. [IrCp*({κ‐C,N‐(NHC‐acetamide−1H)}] (5) (Cp*=pentamethylcyclopentadienyl), has been obtained analogously. [Ir(CI)(CO)2(NHC)] (6) and [Ir({κ‐C,N‐(NHC‐acetamide−1H)}(CO)2] (7) have been prepared by carbonylation of 2 b and 3 c, respectively. The catalytic activity of these complexes has been evaluated in the dehydrogenation of formic acid, under solventless conditions, in the presence of water as a cosolvent, and in a 5 : 2 HCOOH/Et3N mixture, with the best TOF values being obtained in the case of the latter. Stoichiometric experiments suggest COD hydrogenation as the preactivation step.

Diruthenium Catalyst for Hydrogen Production from Aqueous Formic Acid

Diruthenium complexes [{(η6-arene)RuCl}2(μ-κ2:κ2-benztetraimd)]2+ containing the bridging bis-imidazole methane-based ligand {1,4-bis(bis(2-ethyl-5-methyl-1H-imidazol-4-yl)methyl)benzene} (benztetraimd) are synthesized for catalytic formic acid dehydrogenation in water at 90 °C. Catalyst [{(η6-p-cymene)RuCl}2(μ-κ2:κ2-benztetraimd)]2+ [1-Cl2] exhibited a remarkably high turnover frequency (1993 h-1 per Ru atom) and long-term stability over 60 days for formic acid dehydrogenation, while the analogous (η6-benzene)diruthenium and mononuclear catalysts displayed low activity with poor long-term stability. Notably, catalyst [1-Cl2] also displayed an appreciably high turnover number of 93 200 for the bulk-scale reaction. In addition, the in-depth mass and nuclear magnetic resonance investigations under the catalytic and control experimental conditions revealed the active involvement of several crucial catalytic intermediate species, such as Ru-aqua species [{(η6-p-cymene)Ru(H2O)}2(μ-L)]2+ [1-(OH2)2], Ru-formato species [{(η6-p-cymene)Ru(HCOO)}2(μ-L)] [1-(HCOO)2], and Ru-hydrido species [{(η6-p-cymene)Ru(H)}2(μ-L)] [1-(H)2], in the catalytic formic acid dehydrogenation reaction.

Reactivity of Heterobimetallic Ion Pairs in Formic Acid Dehydrogenation

The series of bimetallic complexes (tBuPXCYP)Pd(μ-OC)M(CO)2L (X, Y = CH2, O; M = W, Mo; L = Cp, Tp) catalyzes formic acid decomposition into H2/CO2 in fairly mild conditions (25–50 °C, toluene) without any organic base additives. The catalytic activity of bimetallic complexes increases with CH2-substitution of the O-bridges in the (PXCYP)-frame as well as with the proton-donating ability of the Mo/W hydride. The best result was obtained with (tBuPCP)Pd(μ-OC)Mo(CO)2Cp (3), which gives complete conversion at 2 mol % loading in 30 min at 50 °C (TOF = 100 h–1). During the catalysis, LM(CO)3H and (tBuPXCYP)Pd(OCHO) form as visible intermediates, while the palladium hydride species are also involved in the catalytic cycle. The experimental data show that hydride abstraction/CO2 release from palladium formates (tBuPXCYP)Pd(OCHO) is assisted by −OCHO···H–A hydrogen bonding with excess formic acid or acidic hydride LM(CO)3H. These findings highlight the pivotal role of the formate interaction with Brönsted or Lewis acids at the hydride abstraction/CO2 release step and unify the mechanisms suggested for different catalytic systems.

Carbon bowl-confined subnanometric palladium-gold clusters for formic acid dehydrogenation and hexavalent chromium reduction

Formic acid (FA), a high-value product of CO2 hydrogenation and biomass conversion, is considered a promising liquid organic hydrogen carrier for its high hydrogen content, easy accessibility, and relative stability. The development of an efficient heterogeneous catalyst toward FA dehydrogenation and Cr(VI) reduction by FA is needed to boost its sluggish kinetics but still remains a challenge. Herein, uniformly dispersed subnanometric PdAu alloy clusters (i.e., 0.9 nm) were successfully prepared and confined by amine-functionalized carbon bowls (ACB). By virtue of the tiny size and abundant active sites of PdAu clusters, the promotional effect of surface amine groups, and electronic interaction between subnanometric PdAu clusters and support, this as-prepared PdAu/ACB catalyst exhibits superior catalytic property for additive-free FA dehydrogenation (turnover frequency, 10597 h−1 at 323 K) and Cr(VI) reduction (rate constant, 0.47 min−1 at 298 K) under mild conditions, higher than most of the catalysts reported so far. This study offers insight into the design of efficient and durable catalysts for various catalytic applications in energy and environment.

Au3Pd1 intermetallic compound as single atom catalyst for formic acid decomposition with highly hydrogen selectivity

Developing efficient catalysts for formic acid decomposition has been studied extensively. Herein, the Au3Pd1 intermetallic compound is designed as a single atom catalyst for the dehydrogenation of formic acid. By using density functional theory calculations, the thermodynamic stability, electronic structure, and reaction mechanism for the Au3Pd1 catalyst are systematically investigated, and the surface charge polarization and atom-ordered arrangement were confirmed to play an important role in the efficient formic acid dehydrogenation. The special positively charged Pd single atom on the Au3Pd1 surface becomes the adsorption site of HCOO− and the reaction site for formic acid decomposition. The nearby Au sites suppress the C–O bond cleavage due to their weak interaction with CO∗ and OH∗. As a result, the HCOO− dehydrogenation pathway is predominant on the Pd single atomic sites and the CO formation is well inhibited. This intermetallic-based catalyst can be extended to other systems and provided general guidance for efficient catalyst design.

Selective production of hydrogen isotope gases via PdAg-catalyzed dehydrogenation of formic acid in D2O assisted by surface-grafted amine groups

Hydrogen isotope gases are widely used as deuterium sources in industrial manufacturing processes. It would therefore be beneficial to develop a facile, simple means of selective producing molecular deuterium (D2) and hydrogen deuteride (HD), although reasonable heterogeneous catalytic methodologies are still missing. We previously demonstrated that the hydrogen isotope gases was selectively obtained from formic acid (HCOOH, FA) and D2O using PdAg nanoparticles supported on mesoporous silica (SBA-15) on which amine functional groups had been grafted. In the present work, amine-functionalized carbon was used as an efficient support material to provide a catalyst with improved activity. Employing weakly basic phenylamine groups, D2 was predominantly evolved and the reaction rate was doubled compared with that for our previously reported system. A high degree of correlation between D2 selectivity and the basicity of the grafted amine groups was also observed. The applicability of the present catalytic system was highlighted by in situ deuteration of diphenylacetylene in a solution of FA in D2O, during which deuterated products were obtained with high efficiency.

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.

An interactive study of catalyst and mechanism for electrochemical CO2 reduction to formate on Pd surfaces

Electrochemical CO2 reduction reaction to formate (CO2RRTF) on Pd-based surfaces merits very low overpotentials, yet is challenged with identification of a high-performance catalyst and validation of the reaction pathway. In this work, an interactive study of catalyst and mechanism is presented to address the above bottleneck. On one hand, inspired by preliminary mechanistic understanding of HCOOH ↔ CO2 interconversion at Pd surfaces, a Bi-modified Pd/C with the known high performance towards formic acid dehydrogenation (FAD) is elected as the prototype candidate catalyst for CO2RRTF, exhibiting indeed significantly higher activity, selectivity, durability and extended working potentials. On the other hand, the CO2 chemical hydrogenation mechanism is clarified with monodentate formate being the key intermediate for CO2RRTF on Pd surfaces, by applying isotope labeled ATR-SEIRAS measurement and kinetic analysis in conjunction with DFT calculations. The research paradigm facilitates locating efficient catalysts and advancing mechanistic study for CO2RRTF on Pd surfaces and beyond.

3D printing of cubic zirconia lattice supports for hydrogen production

The demand for hydrogen has extraordinarily grown during the last years, being one of the most attractive forms of fuels to produce green energy. Cubic zirconia ceramics are considered promising catalytic supports, and the additive manufacturing of porous 3D structures based on these ceramics could enhance their catalytic performance. Herein, lightweight highly porous (up to 88%) 3D patterned 8 mol% yttria-stabilized cubic zirconia (8YSZ) scaffolds are manufactured by robocasting from pseudoplastic aqueous-based inks to produce catalytic supports for the hydrogen (H2) production. These scaffolds are thermally treated at temperatures ranging between 1000 and 1400 °C and, hence, mechanically and electrically characterized. 3D 8YSZ structures sintered at 1200 °C, with an appropriate balance between high porosity (86%) and compressive strength (3.7 MPa), are impregnated with palladium (Pd) catalytic nanoparticles and employed in the catalytic dehydrogenation of renewable formic acid (FA) using a fixed-bed reactor. 3D Pd/8YSZ catalyst leads to the continuous production of CO-free H2 with a FA conversion of 32% at T = 55 °C.

Hydrogen Production via Cerium-Promoted Dehydrogenation of Formic Acid Catalyzed by Carbon-Supported Palladium Nanoparticles

Formic acid is a promising hydrogen carrier owing to its high hydrogen density and liquid phase. Therefore, the production of hydrogen from formic acid via catalytic dehydrogenation reaction has been extensively studied. Various methods such as alloying of the active Pd metal with other metals and adding dopants (e.g., the amine-functional group, nitrogen, or metal oxide) have been suggested to enhance the catalytic activities for formic acid dehydrogenation. In this study, we synthesized carbon-supported palladium nanoparticles coexisting with ceria particles and investigated the role of cerium in this reaction over Pd/C catalysts. We made an effort not to change the particle size and the electronic state of Pd significantly while varying Ceria/Pd molar ratios in the catalysts, ruling out their effects on the reaction. Ceria was impregnated on carbon by incipient wetness impregnation; subsequently, Pd was impregnated on Ceria/C by deposition–precipitation. The catalytic tests demonstrated that ceria improved the reaction rate by producing formate anions, the main reactant of this reaction, as it was dissolved by formic acid during the reaction. More importantly, the dissolved cerium ions accelerated the reaction by interacting with the formate anion to change its electronic charge, thereby reducing the activation barrier for C–H bond cleavage. The carbon-supported palladium nanoparticles promoted by cerium could be used to develop a highly efficient hydrogen extraction system from formic acid.

Acetylene functionalized covalent triazine frameworks with AuPd nanoparticles as photocatalysts for hydrogen evolution from formic acid

Photocatalytic dehydrogenation of formic acid (FA) at room temperature is a promising way to meet the increasing demand for hydrogen energy. In this work, we loaded nanoparticles of plasmonic AuPd alloys on the acetylene functionalized covalent triazine frameworks (CTFs) for the design of Mott-Schottky catalysts (AuPd/CTFs) with further application to photocatalytic hydrogen production from FA. Experimental data showed that the introduction of acetylene (-C≡C-) unit and AuPd alloy into the CTF could significantly enhance the performance of hydrogen evolution. The results of photoelectrochemical tests showed that the introduction of carbon-carbon triple bonds and AuPd alloy could adjust the electronic structure of CTF and inhibit charge recombination. Thus, benefiting from these positive effects, the FA photocatalytic decomposition by the obtained AuPd-CTF-EDDBN photocatalyst yielded H2 at a good rate of 10600 μmol·gcat −1·h−1.

Covalent Triazine Framework Encapsulated Ultrafine PdAu Alloy Nanoclusters as Additive-Free Catalysts for Efficient Hydrogen Production from Formic Acid

Dehydrogenation of formic acid (FA) represents a promising route for clean hydrogen production, the economic viability of which, however, is largely hindered by the catalyst inefficiency. Here, ultrafine Au–Pd bimetallic nanoclusters (NCs) confined within the cavities of bipyridyl covalent triazine frameworks (CTFs) are constructed via a metal-nitrogen coordination reduction strategy, which is enabled by the chelation between bidentate nitrogen sites of the bipyridine ligands and metal ion precursors. The resulting CTF-confined PdAu NCs exhibit a high initial turnover frequency up to 12,368 h–1 (333 K) toward the dehydrogenation of FA without any additives. The experimental and theoretical studies disclose that the pyridinic nitrogen sites of CTF not only facilitate the formation of monodisperse small-sized metal NCs via the anchoring and the pore confinement effect but also serve as a proton buffer which can store excess protons and thus suppress the recombination of adsorbed formate and hydrogen on the PdAu alloy surface. These findings would have significant implications for designing high-performance hydrogen production catalysts.

Designing a Robust Palladium Catalyst for Formic Acid Dehydrogenation

Designing a Robust Palladium Catalyst for Formic Acid Dehydrogenation