Selective Decomposition Of Formic Acid Research Articles

Achieving Ultra-High Selectivity to Hydrogen Production from Formic Acid on Pd-Ag Alloys.

Palladium-silver-based alloy catalysts have a great potential for CO-free hydrogen production from formic acid for fuel cell applications. However, the structural factors affecting the selectivity of formic acid decomposition are still debated. Herein, the decomposition pathways of formic acid on Pd-Ag alloys with different atomic configurations have been investigated to identify the alloy structures yielding high H2 selectively. Several PdxAg1-x surface alloys with various compositions were generated on a Pd(111) single crystal; their atomic distribution and electronic structure were determined by a combination of infrared reflection absorption spectroscopy (IRAS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT). It was established that the Ag atoms with Pd neighbors are electronically altered, and the degree of alteration correlates with the number of nearest Pd. Temperature-programmed reaction spectroscopy (TPRS) and DFT demonstrated that the electronically altered Ag domains create a new reaction pathway that selectively dehydrogenates formic acid. In contrast, Pd monomers surrounded by Ag are demonstrated to have a similar reactivity compared to pristine Pd(111), yielding CO and H2O in addition to the dehydrogenation products. However, they bind to the produced CO weaker than pristine Pd, demonstrating an enhancement in resistance to CO poisoning. This work therefore shows that surface Ag domains modified by interaction with subsurface Pd are the key active sites for selective decomposition of formic acid, while surface Pd atoms are detrimental to selectivity. Hence, the decomposition pathways can be tailored for CO-free H2 production on Pd-Ag alloy systems.

Near thermal, selective liberation of hydrogen from formic acid catalysed by copper hydride ate complexes.

A near thermal two-step catalytic cycle for the selective release of hydrogen from formic acid by mononuclear cuprate anions was revealed using multistage mass spectrometry experiments, deuterium labelling and DFT calculations. In gas-phase ion-molecule reactions, mononuclear copper hydride anions [(L)Cu(H)]- (where L = H-, O2CH-, BH4- and CN-) were found to react with formic acid (HCO2H) to yield [(L)Cu(O2CH)]- and H2. The copper formate anions [(L)Cu(O2CH)]- can decarboxylate via collision-induced dissociation (CID) to reform the copper hydride [(L)Cu(H)]-, thereby closing the two-step catalytic cycle. Analogous labelling experiments with d1-formic acid (DCO2H) reveal that the decarboxylation process also occurs spontaneously. A kinetic study was carried out to provide further insights into the species involved in this reaction. Energetics from density functional theory (DFT) calculations show that the key decarboxylation step can occur without CID, thus in support of experimental observations.

有機分子触媒もしくは金属触媒を用いた二酸化炭素変換反応

Technology for the utilization of carbon dioxide (CO2) is expected to gain importance in the near future. This review of studies describes the catalytic conversion of CO2 to chemically useful molecules. Catalysts have been used for the hydrosilylation of CO2, for the synthesis of formic acid (from hydrogen and CO2), for selective decomposition of formic acid to hydrogen and CO2, and for the synthesis of urea from ammonium ions and CO2. These catalytic systems will facilitate the sustainable recycling of CO2.

Photocatalytic selective H2 release from formic acid enabled by CO2 captured carbon nitride

The selective decomposition of formic acid (FA) traditionally needs to be carried out under high temperature with the noble metal-based catalysts. Meanwhile, it also encounters a separation of H2 and CO2 for pure H2 production. The photocatalytic FA dehydrogenation under mild conditions can meet a growing demand for sustainable H2 generation. Here, we reported a photocatalytic selective H2 release from FA decomposition at low temperature for pure H2 production by Pt/g-C3N4. Low-cost and easy-to-obtained urea was utilized to produce carbon nitride as the metal-free semiconductor photocatalyst, along with a photodeposition to obtain Pt/g-C3N4. The electrochemical evidences clearly demonstrate the photocatalytic activity of Pt/g-C3N4 to produce H2 and CO2 in one-step FA decomposition. And, the impedance is the lowest under simulated solar light of 70 mW cm−2 with a faster electron transfer kinetic. Under simulated solar light, H2 production rate is up to 1.59 mmol · h−1 · g−1 for FA with concentration at 2.65 mol l−1, 1700 000 times larger than that under visible light and 1928 times under ultraviolet (UV) light. DFT calculations further elucidate that nitrogen (N) active site at the g-C3N4 has an excellent adsorption towards CO2 molecule capture. Then, H2 molecules are selectively released to simultaneously separate H2 and CO2 in solution. Platinum (Pt) at Pt/g-C3N4 as the catalytic site contributes into the acceleration of H2 production.

Deciphering the role of amine in amino silane-functionalized Pd/rGO catalyst for formic acid decomposition at room temperature

Additive free, selective decomposition of formic acid to hydrogen and carbon dioxide at room temperature is still a challenging catalytic process which often requires noble metal catalyst (Pd, AuPd, AuPt) and sodium formate as an additive. Till date, catalyst design is targeted towards minimum noble metal usage along with incorporation of basic functionalities to produce in situ formate ion (key intermediate for dehydrogenation) from formic acid. In this work, we have studied the catalytic behaviour of amino silane-functionalized graphene oxide (GO) containing palladium nanoparticles for formic acid decomposition in ambient condition. By varying amine functionalization on GO and palladium content, the best performing catalyst was obtained with 5 wt% palladium loading. Additionally, it was observed for the first time that along with stability of a catalyst in reaction medium, its interaction with decomposed products, i.e., carbon dioxide with amine functional groups plays a crucial role in recyclability of a catalyst.

ORGANOMETALLIC GAS-PHASE ION CHEMISTRY AND CATALYSIS: INSIGHTS INTO THE USE OF METAL CATALYSTS TO PROMOTE SELECTIVITY IN THE REACTIONS OF CARBOXYLIC ACIDS AND THEIR DERIVATIVES.

Carboxylic acids are valuable organic substrates as they are widely available, easy to handle, and exhibit structural and functional variety. While they are used in many standard synthetic protocols, over the past two decades numerous studies have explored new modes of metal-mediated reactivity of carboxylic acids and their derivatives. Mass spectrometry-based studies can provide fundamental mechanistic insights into these new modes of reactivity. Here gas-phase models for the following catalytic transformations of carboxylic acids and their derivatives are reviewed: protodecarboxylation; dehydration; decarbonylation; reaction as coordinated bases in C-H bond activation; remote functionalization and decarboxylative C-C bond coupling. In each case the catalytic problem is defined, insights from gas-phase studies are highlighted, comparisons with condensed-phase systems are made and perspectives are reached. Finally, the potential role for mechanistic studies that integrate both gas- and condensed-phase studies is highlighted by recent studies on the discovery of new catalysts for the selective decomposition of formic acid and the invention of the new extrusion-insertion class of reactions for the synthesis of amides, thioamides, and amidines. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Understanding the influence of the composition of the Ag[sbnd]Pd catalysts on the selective formic acid decomposition and subsequent levulinic acid hydrogenation

Formic acid is obtained in equimolar amount with levulinic acid during the hydrolysis of cellulose and thus can be used as a sustainable hydrogen source in the direct levulinic acid hydrogenation towards gamma-valerolactone (biofuel additive). AgPd catalysts prepared by various methods and containing different Ag:Pd ratio were investigated in this context. By combining activity tests, characterization of the main physicochemical properties of the catalysts and DFT study of formic acid decomposition, the key factors responsible for the activity of AgPd catalysts in both the formic acid decomposition and the subsequent hydrogenation of levulinic acid were specified. Pd is shown to be active, but prone to poisoning by CO, while the CO poisoning remains limited on diluted AgPd alloy with strong intermetallic interaction, where its adsorption is very weak thanks to the isolation of Pd atoms. Therefore, the catalyst containing 4%Ag-1%Pd/AlOOH showed the highest selectivity in formic acid decomposition as well as the highest activity in levulinic acid hydrogenation (34% conversion in 5 h at 190 °C).

Models Facilitating the Design of a New Metal‐Organic Framework Catalyst for the Selective Decomposition of Formic Acid into Hydrogen and Carbon Dioxide

AbstractThe front cover artwork for Issue 10/2019 is a collaboration between the O'Hair group (University of Melbourne, Australia) and the Bonačić‐Koutecký group (University of Split, Croatia). The image shows how gas‐phase studies of model systems can be used for the design of MOF based catalysts for the selective decomposition of formic acid into hydrogen and carbon dioxide, a reaction of considerable interest for hydrogen storage applications. See the Full Paper itself at https://doi.org/10.1002/cctc.201900346.

Front Cover: Models Facilitating the Design of a New Metal‐Organic Framework Catalyst for the Selective Decomposition of Formic Acid into Hydrogen and Carbon Dioxide (ChemCatChem 10/2019)

Front Cover: Models Facilitating the Design of a New Metal‐Organic Framework Catalyst for the Selective Decomposition of Formic Acid into Hydrogen and Carbon Dioxide (ChemCatChem 10/2019)

Models Facilitating the Design of a New Metal‐Organic Framework Catalyst for the Selective Decomposition of Formic Acid into Hydrogen and Carbon Dioxide

AbstractHere we describe a new conceptual approach for the design of a heterogeneous metal‐organic framework (MOF) catalyst based on UiO‐67 for the selective decarboxylation of formic acid, a reaction with important applications in hydrogen storage and in situ generation of H2. Models for the {CuH} reactive catalytic site at the organic linker are assessed. In the first model system, gas‐phase mass spectrometry experiments and DFT calculations on a fixed charge bathophen ligated copper hydride complex, [(phen*)Cu(H)]2−, were used to demonstrate that it acts as a catalyst for the selective decomposition of formic acid into H2 and CO2 via a two‐step catalytic cycle. In the first step liberation of H2 to form the carboxylate complex, [(phen*)Cu(O2CH)]2− occurs, which in the second step selectively decomposes via CO2 extrusion to regenerate the hydride complex. DFT calculations on four other model systems showed that changing the catalyst to neutral [(LCu(H)] complexes or embedding it within a MOF results in mechanisms which are essentially identical. Thus catalytic active sites located on the organic linker of a MOF appear to be close to a gas‐phase environment, thereby benefitting from the favorable characteristics of gas‐phase reactions and validating the use of gas‐phase models to design new MOF based catalysts.

How to Translate the [LCu2(H)]+‐Catalysed Selective Decomposition of Formic Acid into H2and CO2from the Gas Phase into a Zeolite.

AbstractTranslating a homogenous catalyst into a heterogeneous catalyst requires a fundamental understanding of how the catalyst “fits” into the zeolite and how the reaction is influenced. Previous studies of bimetallic catalyst design identified a potent copper homobinuclear catalyst, [(L)Cu2(H)]+for the selective decomposition of formic acid. Here, a close interplay between theory and experiment shows how to preserve this selective reactivity within zeolites. Gas‐phase experiments and DFT calculations showed that switching from 1,1‐bis(diphenylphosphino)‐methane ligand to the 1,8‐naphthyridine ligand produced an equally potent catalyst. DFT calculations show that this new catalyst neatly fits into a zeolite which does not perturb reactivity, thus providing a unique example on how “heterogenization” of a homogenous catalyst for the selective catalysed extrusion of carbon dioxide from formic acid can be achieved, with important application in hydrogen storage and in situ generation of H2.

Efficient synthesis of ultrafine Pd nanoparticles on an activated N-doping carbon for the decomposition of formic acid

Palladium nanoparticles (1.88nm) uniformly dispersed on a porous N-doped “leavening” carbon (Pd/NHPC-AC) have been successfully developed, which can be served as a highly active and stable catalyst for the selective decomposition of formic acid under mild conditions. The Pd/NHPC-AC catalyst exhibits enhanced activity for H2 production (TOF=4115h−1 at 60°C) without CO in comparison with Pd/HPC-AC (without nitrogen doping) and Pd/AC under the same reaction conditions. The doping of nitrogen could prevent the Pd nanoparticles from aggregation and leaching from the support surface and therefore improving the reusability of the catalyst.

Boron Nitride‐supported Sub‐nanometer Pd6 Clusters for Formic Acid Decomposition: A DFT Study

AbstractA periodic, self‐consistent planewave DFT study was carried out to explore the potential use of Pd6 clusters supported on a boron nitride sheet as a catalyst for the selective decomposition of formic acid (HCOOH) to CO2 and H2. The competition between formate (HCOO) and carboxyl (COOH) paths on catalytic sites, with different proximities to the support, was studied. Based on energetics alone, the reaction may mainly follow the HCOO route. Slightly lower activation energies were found at the lateral sites of the cluster as compared to top face sites. This is particularly true for the bidentate to monodentate HCOO conversion. Through comparison of results with similar studies on HCOOH decomposition on extended Pd surfaces, it was demonstrated that the existence of undercoordinated sites in the sub‐nanometer cluster could play a key role in preferentially stabilizing HCOO over COOH, which is a common CO precursor in this reaction. A hydrogen spillover mechanism was also investigated; migration toward the boron nitride support is not favorable, at least in the early stages of the reaction. However, hydrogen diffusion on the cluster has low barriers compared to those involved in formic acid decomposition.

Dehydrogenation of Formic Acid Catalyzed by a Ruthenium Complex with an N,N'-Diimine Ligand.

We report a ruthenium complex containing an N,N'-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. A turnover frequency of 12 000 h-1 and a turnover number of 350 000 at 90 °C were achieved in the HCOOH/HCOONa aqueous solution. Efficient production of high-pressure H2 and CO2 (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO. Mechanistic studies by NMR and DFT calculations indicate that there may be two competitive pathways for the key hydride transfer rate-determining step in the catalytic process.

Simple Continuous High‐Pressure Hydrogen Production and Separation System from Formic Acid under Mild Temperatures

AbstractA simple and continuous high‐pressure (>120 MPa) hydrogen production system was developed by the selective decomposition of formic acid at 80 °C using an iridium complex as a catalyst, with a view to its application in future hydrogen fuel filling stations. The system is devoid of any compressing system. The described method can provide high‐pressure H2 with 85 % purity after applying an effective gas–liquid separation process to separate the generated gas obtained from the decomposition of formic acid (H2/CO2=1:1). The efficiency of the catalyst lies with its high turnover frequency (1800 h−1 at 40 MPa) to produce high‐pressure H2 with a good lifetime of >40 h. Interestingly, only very low levels carbon monoxide (less than 6 vol ppm) were detected in the generated gas, even at 120 MPa.

Hydrogenation and dehydrogenation iron pincer catalysts capable of metal-ligand cooperation by aromatization/dearomatization.

The substitution of expensive and potentially toxic noble-metal catalysts by cheap, abundant, environmentally benign, and less toxic metals is highly desirable and in line with green chemistry guidelines. We have recently discovered a new type of metal-ligand cooperation, which is based on the reversible dearomatization/aromatization of different heteroaromatic ligand cores caused by deprotonation/protonation of the ligand. More specifically, we have studied complexes of various transition metals (Ru, Fe, Co, Rh, Ir, Ni, Pd, Pt, and Re) bearing pyridine- and bipyridine-based PNP and PNN pincer ligands, which have slightly acidic methylene protons. In addition, we have discovered long-range metal-ligand cooperation in acridine-based pincer ligands, where the cooperation takes place at the electrophilic C-9 position of the acridine moiety leading to dearomatization of its middle ring. This type of metal-ligand cooperation was used for the activation of chemical bonds, including H-H, C-H (sp(2) and sp(3)), O-H, N-H, and B-H bonds. This unusual reactivity likely takes place in various catalytic hydrogenation, dehydrogenation, and related reactions. In this Account, we summarize our studies on novel bifunctional iron PNP and PNN pincer complexes, which were designed on the basis of their ruthenium congeners. Iron PNP pincer complexes serve as efficient (pre)catalysts for hydrogenation and dehydrogenation reactions under remarkably mild conditions. Their catalytic applications include atom-efficient and industrially important hydrogenation reactions of ketones, aldehydes, and esters to the corresponding alcohols. Moreover, they catalyze the hydrogenation of carbon dioxide to sodium formate in the presence of sodium hydroxide, the selective decomposition of formic acid to carbon dioxide and hydrogen, and the E-selective semihydrogenation of alkynes to give E-alkenes. These catalysts feature, compared to other iron-based catalysts, very high catalytic activities which in some cases can even exceed those of state-of-the-art noble-metal catalysts. For the iron PNP systems, we describe the synthesis of the pyridine- and acridine-based PNP iron complexes and their performances and limitations in catalytic reactions, and we present studies on their reactivity with relevance to their catalytic mechanisms. In the case of the bipyridine-based PNN system, we summarize the synthesis of new complexes and describe studies on the noninnocence of the methylene position, which can be reversibly deprotonated, as well as on the noninnocence of the bipyridine unit. Overall, this Account underlines that the combination of cheap and abundant iron with ligands that are capable of metal-ligand cooperation can result in the development of novel, versatile, and efficient catalysts for atom-efficient catalytic reactions.

Selective Decomposition of Formic Acid over Immobilized Catalysts

A highly selective decomposition of formic acid in aqueous medium was achieved with immobilized catalysts. In the gas product of all of the experiments, only hydrogen and carbon dioxide were detected. The activity of different immobilized catalysts for the decomposition of formic acid was checked, and the highest turnover frequency (TOF) was observed using Pd–S–SiO2. Moreover, we have found that the addition of sulfates could significantly promote the activities of mercapto-functionalized catalysts by 30–70%, which is attractive for practical applications.

Simple and recyclable ionic liquid based system for the selective decomposition of formic acid to hydrogen and carbon dioxide

Exploitation of hydrogen as an energy carrier requires the development of systems for its storage and delivery. Formic acid has been proposed as valuable hydrogen carrier compound, due to its relatively high hydrogen content (53 g L−1), the latter being easily and cleanly released in catalytic reactions under mild conditions (HCOOH → H2 + CO2). Ionic liquids are interesting solvents for homogeneous catalyzed formic acid decomposition systems as their extremely low volatility avoids solvent contamination of the produced hydrogen stream. In this paper an outstandingly simple, robust and active catalyst system is presented, namely RuCl3 dissolved in 1-ethyl-2,3-dimethylimidazolium acetate (RuCl3/[EMMIM][OAc]). This system proved to be fully recyclable over 10 times. Turnover frequencies (TOF) of 150 h−1 and 850 h−1 were obtained at 80 °C and 120 °C, respectively.

Selective decomposition of formic acid on molybdenum carbide: A new reaction pathway

Selective decomposition of formic acid is important as a prototype to study selective bond cleavage of oxygenates. We demonstrate that carbon-modified Mo(1 1 0), C–Mo(1 1 0), is up to 15 times more selective for the dehydrogenation of formic acid than Mo(1 1 0). Reflection absorption infrared spectroscopy (RAIRS) indicates that carbidic carbon blocks active sites for C–O bond cleavage, decreasing the rate of dehydration. Steady-state reactive molecular beam scattering (RMBS) shows that dehydration is the dominant reaction pathway on clean Mo(1 1 0), while C–Mo(1 1 0) selectively promotes dehydrogenation. Kinetic analysis of RMBS data reveals that formic acid dehydrogenation on Mo(1 1 0) has an activation energy of 34.4 ± 3.3 kJ mol −1 while the C–Mo(1 1 0) surface promotes distinct pathways for dehydrogenation with an activation energy of only 12.8 ± 1.0 kJ mol −1. RAIRS spectra suggest the new pathways include the formation of monodentate formate, and at temperatures of 500 K and greater, direct activation of the C–H bond to form carboxyl, both of which decompose via a CO 2 δ - intermediate to evolve CO 2 and H 2.

A Viable Hydrogen‐Storage System Based On Selective Formic Acid Decomposition with a Ruthenium Catalyst

Ameisensäure kann als Speicherform für Wasserstoff genutzt werden: Dabei hilft ein homogenkatalytisches System auf der Grundlage wasserlöslicher Rutheniumkomplexe (Ru/TPPTS; TPPTS=meta-trisulfoniertes Triphenylphosphan), das HCOOH unter milden Bedingungen selektiv in H2 und CO2 zerlegt und über einen großen Druckbereich hoch reines H2 freisetzt.