Decomposition Of Formic Acid Research Articles

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.

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.

Fast hydrogen evolution by formic acid decomposition over AuPd/TiO2-NC with enhanced stability

Fast hydrogen evolution by formic acid decomposition over AuPd/TiO2-NC with enhanced stability

Tailored synthesis of a palladium catalyst supported on nitrogen-doped carbon nanotubes for gas-phase formic acid decomposition: A strong influence of a way of nitrogen doping

Palladium catalysts supported on different nitrogen-containing carbon nanotubes (N-CNTs) were successfully used in the continuous gas-phase formic acid decomposition for hydrogen production. A strong influence of a way of carbon tubes doping by nitrogen on the activity of catalysts comprising metallic nanoparticles of ca. 1 nm in size and single-atom Pd2+ species was found. A key role of the single-atom species, demonstrating excellent stability in various chemically aggressive media, in the catalyst activity was discovered when bamboo-like N-CNTs synthesized by catalytic chemical vapor deposition were used as a support. A substantial increase in the activity of Pd nanoparticles was achieved by the use of N-СNTs prepared by the post-treatment of oxidized multiwalled carbon nanotubes by ammonia resulting in the formation of the dominating surface amine groups. The combination of the electron-rich palladium nanoparticles and surface amine groups leads to an increase in the TOF value by a factor of 7 at 70 °C. The catalyst operates stable at >99 % selectivity to hydrogen with the mass specific performance 200 l H2/gPd ⋅ h.

Hydrogen-free carbon monoxide production through decomposition of formic acid over a HPW/TiO2 catalyst

The dehydration of formic acid over supported phosphotungstic acid (H3PW12O40, HPW) catalysts was investigated for the production of hydrogen-free carbon monoxide (CO). The variations in the support type (SiO2, Al2O3, ZrO2, and TiO2) and HPW content (0.0–20.0 wt.%) affect the acidity of catalysts, which was demonstrated by the temperature-programed desorption of iso-propanol (IPA-TPD) and pyridine-adsorbed infrared spectroscopy (Py-IR). The catalytic activity in formic acid dehydration exhibited a volcano-type distribution in accordance with the HPW content and was maximized at 15 wt.% loading. Furthermore, the catalytic activity was more closely related to the density of Brønsted acids than that of Lewis acids and inversely proportional to the peak temperature of propylene desorption during IPA-TPD. The strongly adsorbed H2O on the catalysts, which is generated during formic acid dehydration, induces deactivation of the catalyst, particularly at lower reaction temperatures (<230 °C).

Hydrogen production from formic acid in fluidized bed made out of Ni-cenosphere catalyst

This research presents a method of hydrogen production from formic acid with the use of fluidized bed technology. The core-shell catalyst was developed by applying the Ni layer on cenospheres via a technique of gaseous deposition. The efficiency of the decomposition of formic acid was tested continuously in the range of 200–500 °C. An analytical method, based on infrared spectroscopy, allowing the continuous monitoring of the concentration of products in the gas phase has been developed. A 67% yield of hydrogen was achieved at 233 °C. The proposed solution in a fluidized bed has been compared with other methods of obtaining hydrogen from formic acid. The most important advantages of the proposed solutions are on-demand hydrogen generation; the use of an energy carrier that can be obtained from biomass or CO2; simplicity of the process including easy control of the process temperature; repeatability; ease of scaling the fluidized process; the possibility of continuous monitoring of the products of the process; high efficiency of hydrogen generation per unit volume of the reactor.

High Chemical Potential Driven Amorphization of Pd-based Nanoalloys.

Amorphous metals and alloys are promising candidates for superior catalysts in many catalytic and electrocatalytic reactions. It is of great urgency to develop a general method to construct amorphous alloys and further clarify the growth mechanism in a wet-chemical system. Herein, inspired by the conservation of energy during the crystallization process, amorphous PdCu nanoalloys have been successfully synthesized by promoting the chemical potential of the building blocks in solution. Benefiting from the abundant active sites and enhanced corrosion resistance, the synthesized amorphous PdCu nanostructures exhibit superior catalytic activity and durability over the face-centered cubic one in formic acid decomposition reaction. More importantly, the successful fabrications of amorphous PdFe, PdCo, and PdNi further demonstrate the universality of the above strategy. This proposed strategy is promising to diversify the amorphous family.

A Coverage Self-Consistent Microkinetic Model for Vapor-Phase Formic Acid Decomposition over Pd/C Catalysts

An iterative approach utilizing density functional theory (DFT, PW91-GGA)-informed mean-field microkinetic models and reaction kinetics experiments is used to determine the reaction mechanism and the active site for formic acid (HCOOH, FA) decomposition over a Pd/C catalyst. Models parametrized using DFT energetics on clean Pd(100) and Pd(111) required large corrections to the DFT energetics for capturing our experimental data. Further, both Pd(111) and Pd(100) models predicted a high coverage of adsorbed CO (CO*), inconsistent with the assumption of a clean surface at which the rate parameters for these models were calculated. To better represent the active site under reaction conditions and explicitly account for the presence of CO*, subsequent microkinetic models were formulated using DFT energetics that were calculated on partially (5/9 ML) CO*-covered Pd (111) and (100) facets. Upon parameter adjustment, the resultant 5/9 ML CO*-covered Pd(100) model, although consistent in terms of CO* coverage, was unable to capture the dehydration path measured in the experiments and was, therefore, deemed not to offer an accurate representation of the active site for FA decomposition over Pd/C. In contrast, a partially CO*-covered Pd(111) model was better at representing the catalytic active site, as in addition to being consistent in terms of CO* coverages, it required small adjustments of the DFT parameters to accurately capture the experimental data set (both dehydrogenation and dehydration). Our results suggest that the reaction occurs via the spectroscopically elusive carboxyl (COOH*) intermediate and that spectator CO*-assisted decomposition pathways play an important role under typical experimental conditions. Further, our study highlights the importance of striving for coverage self-consistent microkinetic models and for including spectator-assisted mechanisms in order to develop an improved picture of the active site under reaction conditions.

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.

Ru Catalysts Supported on Bamboo-like N-Doped Carbon Nanotubes: Activity and Stability in Oxidizing and Reducing Environment.

The catalysts with platinum-group metals on nanostructured carbons have been a very active field of research, but the studies were mainly limited to Pt and Pd. Here, Ru catalysts based on nitrogen-doped carbon nanotubes (N-CNTs) have been prepared and thoroughly characterized; Ru loading was kept constant (3 wt.%), while the degree of N-doping was varied (from 0 to 4.8 at.%) to evaluate its influence on the state of supported metal. Using the N-CNTs afforded ultrafine Ru particles (<2 nm) and allowed a portion of Ru to be stabilized in an atomic state. The presence of Ru single atoms in Ru/N-CNTs expectedly increased catalytic activity and selectivity in the formic acid decomposition (FAD) but had no effect in catalytic wet air oxidation (CWAO) of phenol, thus arguing against a key role of single-atom catalysis in the latter case. A remarkable difference between these two reactions was also found in regard to catalyst stability. In the course of FAD, no changes in the support or supported species or reaction rate were observed even at a high temperature (150 °C). In CWAO, although 100% conversions were still achievable in repeated runs, the oxidizing environment caused partial destruction of N-CNTs and progressive deactivation of the Ru surface by carbonaceous deposits. These findings add important new knowledge about the properties and applicability of Ru@C nanosystems.

Mechanistic insights into hydrogen production from formic acid catalyzed by Pd@N-doped graphene: The role of the nitrogen dopant

The catalytic decomposition of formic acid (HCOOH) is a crucial process for hydrogen production technologies. Herein, periodic density functional theory (DFT) calculations were employed to explore the effect of N-doping on the decomposition of formic acid. We designed a series of single Pd-atoms deposited in the single vacancy of N-doped graphene sheets, namely Pd-DGr, Pd–N1Gr, Pd–N2Gr, and Pd–N3Gr, as the proposed catalysts. Our findings show that H2 production from HCOOH dehydrogenation on these surfaces proceeds via the formate (HCOO) pathway (Path-I) rather than the carboxylate (COOH) pathway (Path-II). Furthermore, the Pd–N3Gr catalyst shows the greatest catalytic reactivity toward HCOOH dehydrogenation via Path-I, requiring an activation energy (Ea) of 0.38 eV.On the other hand, the undesirable dehydration of HCOOH to carbon monoxide (CO) through COOH (Path-IIIA) or formyl (HCO) (Path-IIIB) intermediates is unlikely to occur on Pd–N3Gr due to a large activation energy. We found that the active species on the catalyst surface increased with N-doping concentration. Additionally, microkinetic simulations of the HCOOH decomposition on these surfaces confirmed the high activity and selectivity of the Pd–N3Gr catalyst toward HCOOH dehydrogenation (Path-I). These calculated results highlight that the Pd–N3Gr catalyst is a promising candidate for the formic acid decomposition reaction to yield hydrogen.

Highly Efficient Photocatalytic Syngas Production from Formic Acid Using Iron-Porphyrins as Catalysts Integrated with CdS/CNTs Heterojunctions under Visible Light

Syngas (H2 + CO) is a compatible fuel for internal combustion engines, or it can be transformed to liquid fuels, which can help overcome future energy crises sustainably. In this study, we report an inexpensive and highly active photocatalytic system for production of syngas from formic acid under ambient conditions. The photocatalytic system comprising CdS/CNT hybrids and a porphyrin-based catalyst showed remarkable H2 and CO evolution at ambient conditions. Using monochromatic light (420 nm), the highest values of apparent quantum yields reached 22.8 and 12.5% for H2 and CO, respectively. Photoluminescence spectra and photocurrent responses proved the efficient electron transfer between the hybrid photosensitizer and the molecular catalyst, which enhanced the performance of the present photocatalytic system. Mechanistic insights regarding the molecular catalyst were obtained using cyclic voltammetry, inferring the generation of Fe(I) species as a critical step in the photocatalytic decomposition of formic acid.

Disclosing the leaching behaviour of Pd@CMK3 catalysts in formic acid decomposition by electron tomography.

Supported nanocatalysts exhibit different performances in batch and fixed bed reactors for a wide range of liquid phase catalytic reactions due to differences in metal leaching. To investigate this leaching process and its influence on the catalytic performance, a quantitative 3D characterization of the particle size and the particle distribution is important to follow the structural evolution of the active metal catalysts supported on porous materials during the reaction. In this work, electron tomography has been applied to uncover leaching and redeposition of a Pd@CMK3 catalyst during formic acid decomposition in batch and fixed bed reactors. The 3D distribution of Pd NPs on the mesoporous carbon CMK3 has been determined by a quantitative tomographic analysis and the determined structural changes are correlated with the observed differences in activity and stability of formic acid decomposition using batch and fixed bed reactors.

Phase-dependent selectivity control over TiO2 in the photocatalytic oxidation of bio-polyols.

Photocatalytic oxidation shows great potential in the valorization of biomass under mild conditions, while the selectivity control is particularly challenging for the complex and reactive bio-polyols. Herein, we report a selective photocatalytic process to convert bio-polyols into formic acid (FA) or carbon monoxide (CO) by controlling the phase of TiO2. The bio-polyols are facially oxidized to formic acid (FA) which is stable over rutile and could be dehydrated to CO over anatase TiO2. Through controlling the phase, FA or CO could be obtained from a wide range of bio-polyols with selectivity up to 63% or 52%. Our studies elucidate that the phase-dependent selectivity is essentially derived from the difference in the adsorption configuration of FA. In situ Fourier transform infrared spectroscopy (FTIR) and density functional (DFT) calculations were used to study the FA decomposition process on the surface of TiO2. The phase-dependent FA decomposition is mainly derived from the different surface geometry, which affects the configuration of FA adsorption. Molecular adsorbed FA on anatase favors the dehydration of FA to CO while bidentate dissociated adsorption of FA on the rutile phase is inert to be further converted. This work provides a new horizon to the design of photocatalytic systems for biomass conversion.

Boosting photocatalytic conversion of formic acid to CO over P-doped CdS.

In this work, NaH2PO2, Na2S2O3 and CdCl2 were used to synthesize P-doped CdS samples for the photocatalytic decomposition of formic acid to CO reaction. The CO production rates and selectivity of P-doped CdS are as high as 24.5 mmol g-1 h-1 and 92.4%, in which the rate is 7 times higher than that of the pure CdS. Multiple characterizations show that the P-doping increases the specific surface area, widens the band gap and shifts the energy band position of CdS, resulting in enhanced photocatalytic activity.

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.

Highly efficient photocatalytic formic acid decomposition to syngas under visible light using CdS nanorods integrated with crystalline W2N3 nanosheets

An efficient photocatalytic system was constructed by combining crystalline W2N3 nanosheets and CdS nanorods for formic acid decomposition to produce syngas under visible light.

Photo-enhanced dehydrogenation of formic acid on Pd-based hybrid plasmonic nanostructures.

Coupling visible light with Pd-based hybrid plasmonic nanostructures has effectively enhanced formic acid (FA) dehydrogenation at room temperature. Unlike conventional heating to achieve higher product yield, the plasmonic effect supplies a unique surface environment through the local electromagnetic field and hot charge carriers, avoiding unfavorable energy consumption and attenuated selectivity. In this minireview, we summarized the latest advances in plasmon-enhanced FA dehydrogenation, including geometry/size-dependent dehydrogenation activities, and further catalytic enhancement by coupling local surface plasmon resonance (LSPR) with Fermi level engineering or alloying effect. Furthermore, some representative cases were taken to interpret the mechanisms of hot charge carriers and the local electromagnetic field on molecular adsorption/activation. Finally, a summary of current limitations and future directions was outlined from the perspectives of mechanism and materials design for the field of plasmon-enhanced FA decomposition.

Atomic-Layer-Deposition Derived Pt subnano Clusters on the (110) Facet of Hexagonal Al2O3 Plates: Efficient for Formic Acid Decomposition and Water Gas Shift

The Pt subnano clusters dispersed on the (110) facet of regularly shaped hexagonal Al2O3 plates were fabricated via an atomic layer deposition approach. The resulting material contains Pt loading as low as 0.07 wt %; the interfacial structure exhibits nearly full CO conversion for water gas shift reaction at 210 °C, and the turnover frequency (TOF) of CO is as high as 2.1 s–1, outperforming most of the systems reported. The same interfacial structure was also found to be highly active for catalytic decomposition of formic acid (FA), with full FA conversion (with little CO product) and the TOF being 1.02 s–1. Further characterizations together with density functional theory simulations elucidate that the superior catalytic performances are attributed to the unique interfacial structure and the synergism between the small Pt clusters and the Al2O3 (110) substrate, leading to lower energy barriers for the *COOH intermediate formation over the ultrafine Pt ensembles and the hydroxylation over the Al2O3 (110) substrate close to the Pt entities. Both are favorable for the evolution of *COOH intermediate and the reaction between *COOH and neighbor OH species. The current study provides insights into the effectiveness in generating high-performance catalytic material for clean energy production and modulation through precise control of the metal entity dimension and the oxide substrate engineering to achieve specific facet exposure.

One-Pot direct reductive amination of furfural over Pd@CNTs

N-substituted furfuryl amines (secondary amines) are important class of organic compounds which are primarily used in making agricultural and pharmaceutical intermediates. The main objective of the present study is to develop the use of bio-based ennvironment friendly chemical such as furfural for selective one-step process for N-substituted furfuryl amines production using formic acid (FA) as a hydrogen source over heterogeneous catalyst. Rh-CNTs, Pd-CNTs, Pd-Al2O3, and Pd-HT catalysts were prepared using a facile combination of wet impregnation, followed by freeze-drying method and used for the synthesis of N-substituted furfuryl amines. The as-synthesized and used catalysts were characterized by various physico-chemical characterization methods to investigate the role of support in promoting activity and selectivity of catalyst. Under optimised condition, Pd-CNTs catalyst in methanol was found to convert furfural and aniline almost completely to N-(furan-2-ylmethyl)aniline. Moreover, Pd-CNTs catalyst showed outstanding activity towards complete decomposition of FA to H2 and CO2, giving a high yield of N-(furan-2-ylmethyl)aniline (>99%) from hydrogenation of furfural and aniline. The catalyst also showed good recyclability and worked for at least three consecutive recycling runs without lossing activity. The effect of reaction parameters viz. temperature, reaction time, and FA concentration, on the conversion and selecivity were studied in detail.