For Formic Acid Research Articles

Lewis Acidic VOx Engineered PdAu Nanocatalysts for Efficient Formic Acid Dehydrogenation

AbstractThe development of high‐performance catalysts for formic acid (FA) dehydrogenation is of extreme significance to the successful production of hydrogen under ambient conditions. Despite some encouraging progress, their activity is still unsatisfied than needed. In this work, it is presented that Lewis acidic VOx sites engineered ultrafine PdAu nanoclusters (PdAu‐VOx) perform perfectly for hydrogen production from FA dehydrogenation. Strikingly, the best catalyst — PdAu‐VOx embed in amino‐functionalized hollow mesoporous support (PdAu‐VOx/NHMS) discloses an impressive initial turnover frequency of 14155 h−1 and a low activation energy of 31.2 kJ mol−1 without additives at room temperature, and maintains 100% selectivity and conversion in the tenth cycle reaction. Mechanistic investigations illustrate that VOx species can serve as the Lewis acid sites, which not only regulate the adsorption strength of reactant and intermediate on PdAu, but also reinforce the C─H bond activation within FA molecule, thereby promoting the reaction kinetics for efficient hydrogen production. This work thus provides a strategy for the development of new‐style heterogeneous catalysts with Lewis acid‐base sites applied to a variety of energy‐related catalytic reactions.

Synthesis of Cr(OH)3/ZrO2@Co-based metal-organic framework from waste poly(ethylene terephthalate) for hydrogen production via formic acid dehydrogenation at low temperature

Recycling waste polyethylene terephthalate (PET) bottles into value-added ligand materials for synthesizing metal-organic frameworks (MOFs) derived catalysts is an eco-friendly and economically viable process. The waste PET bottles were readily broken down into 1,4-benzenedicarboxylic acid (BDC) ligands in a highly alkaline environment. Herein, we fabricated a Co@Cr(OH)3/ZrO2 catalyst via the carbonization of PET-derived UiO-66 metal-organic frameworks for the catalytic dehydrogenation of formic acid at low temperatures. The as-prepared Co@Cr(OH)3/ZrO2 catalyst provides a turnover frequency of 7685 h−1 for hydrogen generation (120 mL in 1.5 min) at ambient temperature. This is due to the uniform dispersion of the fine metal nanoparticle (NPs) (Co NPs, ∼3.75 nm) and the synergistic effect of the Co NPs and Cr(OH)3/ZrO2 supports. In addition, the characterization results indicate that porous Zr-MOFs may effectively enclose tiny particles, which is favorable for enhanced dehydrogenation performance. In addition, the Co@Cr(OH)3/ZrO2 catalysts demonstrated excellent stability against aggregation and were recyclable over seven cycles without any significant catalytic loss. Thus, this study provides a sustainable methodology for the development of MOF-derived, effective, and stable catalysts for formic acid dehydrogenation towards hydrogen production.

Coverage enhancement accelerates acidic CO2 electrolysis at ampere-level current with high energy and carbon efficiencies

Acidic CO2 electroreduction (CO2R) using renewable electricity holds promise for high-efficiency generation of storable liquid chemicals with up to 100% CO2 utilization. However, the strong parasitic hydrogen evolution reaction (HER) limits its selectivity and energy efficiency (EE), especially at ampere-level current densities. Here we present that enhancing CO2R intermediate coverage on catalysts promotes CO2R and concurrently suppresses HER. We identified and engineered robust Cu6Sn5 catalysts with strong *OCHO affinity and weak *H binding, achieving 91% Faradaic efficiency (FE) for formic acid (FA) production at 1.2 A cm−2 and pH 1. Notably, the single-pass carbon efficiency reaches a new benchmark of 77.4% at 0.5 A cm−2 over 300 hours. In situ electrochemical Fourier-transform infrared spectroscopy revealed Cu6Sn5 enhances *OCHO coverage ~2.8× compared to Sn at pH 1. Using a cation-free, solid-state-electrolyte-based membrane-electrode-assembly, we produce 0.36 M pure FA at 88% FE over 130 hours with a marked full-cell EE of 37%.

Formic Acid Dehydrogenation through Ligand Design Strategy of Amidation in Half-Sandwich Ir Complexes.

A series of Cp*Ir (Cp* = pentamethylcyclopentadienyl) complexes with amidated 8-aminoquinoline ligands were synthesized and tested for formic acid (FA) dehydrogenation. These complexes showed improved activities compared to pristine 8-anminquinoline (L1). Specially, amidation changed the outer coordination sphere of the complex (3) bearing N-8-quinolinylformamide (L3), and 3 was proved to be a proton-responsive catalyst. Our experimental results and DFT calculations demonstrated that the deprotonated carbanion in L3 could interact with a water molecule to stabilize the transition states and lower the reaction energy barrier, which improved the reaction activity. A turnover frequency of 206250 h-1 was achieved by 3 under optimized conditions. This study presents a method to develop new ligands and modify the existing ligands for efficient FA dehydrogenation.

Synergistic Combination of Fermi Level Equilibrium and Plasmonic Effect for Formic Acid Dehydrogenation.

Developing an efficient catalyst for formic acid (FA) dehydrogenation is a promising strategy for safe hydrogen storage and transportation. Herein, we successfully developed trimetallic NiAuPd heterogeneous catalysts through a galvanic replacement reaction and a subsequent chemical reduction process to boost hydrogen generation from FA decomposition at room temperature by coupling Fermi level engineering with plasmonic effect. We demonstrated that Ni worked as an electron reservoir to donate electrons to Au and Pd driven by Fermi level equilibrium whereas plasmonic Au served as an optical absorber to generate energetic hot electrons and a charge-redistribution mediator. Ni and Au worked cooperatively to promote the charge heterogeneity of surface-active Pd sites, leading to enhanced chemisorption of formate-related intermediates and eventually outstanding activity (342 mmol g-1 h-1 ) compared with bimetallic counterpart. This work offers excellent insight into the rational design of efficient catalysts for practical hydrogen energy exploitation.

Pd nanoparticles confined in pure Silicalite-2 zeolite with enhanced catalytic performance for the dehydrogenation of formic acid at room temperature

The activity and stability of metal nanoparticles (NPS) have become a focus of attention in various important reactions. In this study, pure Silicalite-2 (S-2) zeolite with highly skeletal symmetry was synthesized by a facile method, and sub-nanometer Pd NPs were successfully confined in S-2 zeolite by one-step process. The pore structure of S-2 zeolite posted steric physical barriers against the migration of Pd NPs. Meanwhile, the strong interaction between the active Pd and the substrate provides a chemical microenvironment for accelerating the reaction. The obtained Pd3@S-2 with Pd NPs particle size of 1.5 nm show a conversion frequency (TOF) of 2009 h−1 for formic acid (FA) decomposition at 30 °C, and have 100 % H2 selectivity, excellent cycle stability and thermal stability.

Formic acid-to-hydrogen on Pd/AC catalysts: Kinetic study with catalytic deactivation

A kinetic model for formic acid (FA) decomposition over a commercial 10 wt% Pd/AC catalyst has been developed to describe the hydrogen production and to understand the deactivation mechanism. The kinetic data were obtained in a batch slurry reactor in absence of mass transfer limitation at: CFA,0 = 0.25–2 M, CCAT = 1 g L−1, T = 25–85 ºC and P = 1 atm. The catalyst stability was studied in successive cycles at different temperatures. Fresh, used and regenerated Pd/AC catalysts were deeply characterized to gain insight into the activity, selectivity and stability. H2 and CO2 were the only reaction products detected. The reaction follows a first order kinetic for FA while the activity shows exponential decay with the initial FA concentration and reaction temperature. This paper represents a step forward in the on-site hydrogen production technology by using FA as liquid organic hydrogen carrier.

Facile construction of a highly dispersed PdCo nanocatalyst supported on NH2-UiO-66-derived N/O co-doped carbon for hydrogen evolution from formic acid

Rational design of catalysts with a high activity and low cost is crucial but still challenging for formic acid (FA) as a hydrogen storage material. Herein, PdCo-bimetallic particles were evenly dispersed on N/O co-doped porous carbon, which is achieved through the one-step pyrolysis NH2-UiO-66 strategy. The evaluation test demonstrated that the prepared catalysts had high activity and selectivity for the decomposition of FA. The turnover frequency (TOF) of FA decomposition catalyzed by Pd4Co1/CN–O-800 at 30 °C was 2425 h−1 (TOF at 50 °C was 4587 h−1) and the selectivity of hydrogen was 100%. Structural characterizations combined with detailed theoretical calculation results reveal that the constructed N/O co-doped system endows the bimetallic catalyst with abundant catalytic sites and strong metal-support interaction, thereby achieving remarkable catalytic performance. The results provide ideas for the design of efficient FA dehydrogenation catalysts and offer theoretical guidance to N/O co-doped carbon materials.

Experimental and Theoretical Studies of Ultrafine Pd-Based Biochar Catalyst for Dehydrogenation of Formic Acid and Application of In Situ Hydrogenation.

In this work, a novel "foaming" strategy uses sodium bicarbonate (NaHCO3) and ammonium oxalate ((NH4)2C2O4) as the foaming agent, turning biomass-derived carboxymethyl cellulose (CMC) into N-doped porous carbon. Highly active palladium nanoparticles (Pd NPs) immobilized on nitrogen-doped porous carbon (Pd@MC(2)-P) are produced through a phosphate-mediation approach. The phosphoric acid (H3PO4) becomes the key to the synthesis of highly dispersed ultrafine Pd NPs on active Pd-cluster-edge (the edge of the Pd-cluster-100 and Pd-cluster-111 surfaces). The Pd@MC(2)-P exhibits high activity for formic acid (FA) dehydrogenation with an initial TOFg of 971 h-1 at room temperature. The subsequent hydrogenation of phenol using FA as an in situ hydrogen source on Pd@MC(2)-P and the highly efficient hydrogenation of phenol to cyclohexanone reaches more than 90% selectivity and 80% conversion. Density functional theory (DFT) calculations reveal that the reduced H poisoning and more exposed (100) surface over Pd nanoparticles are the keys to the Pd nanoparticles' high activity.

Electro-Oxidation of Glycerol into Formic Acid by Nickel-Copper Electrocatalysts

Herein, non-precious metallic nickel-copper electrocatalysts were synthesized for electro-oxidation of glycerol in alkaline electrolytes. Activated carbon felt (ACF) is used as a supporting material because of its good conductivity, chemical inertness, and porous structure which is conducive to the transport of the reactants/electrons. The structural features of the catalysts were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The electrochemical activity of the catalysts was revealed by cyclic voltammetry, linear sweeping voltammetry, and chronoamperometry. The electrochemical results show that the Cu1Ni1@ACF catalyst possesses the highest current density of 1.31 mA cm−2 at 1.895 V. High-performance liquid chromatography results show that the as-prepared catalysts have high selectivities for formic acid (FA). Especially, the Cu1Ni1@ACF catalyst yields a selectivity of 97.4% for FA, which has so far been the largest value reported in the literature. Additionally, the effects of applied potentials and reaction time on product selectivity were studied.

Strategic examination of the classical catalysis of formic acid decomposition for intermittent hydrogen production, storage and supply: A review

Practically, an ideal catalyst for Formic acid-decomposition is one that best suits the reaction and significantly lowers its activation energy and improves the reaction rate under favourable conditions. Several catalysts for Formic Acid (FA)-decomposition reactions were examined. Based on the volcano curve and the potential of copper to give high hydrogen yields, emphasis was placed on a Cu-catalysed reaction as potential system for sustainable hydrogen production. Some recent advances in hydrogen production from formic acid were discussed and an effective system for FA-decomposition for hydrogen production was proposed. Since helium can be stored in weather balloons and weighs almost the same as hydrogen, a hydrogen buffer made from polyester fabric and coated with polyurethane or a hydrogen cylinder/tube was proposed for storing hydrogen for use as transport-fuel. Also, due to the nature of the mechanisms/pathways describing FA-conversion reactions at the sites or surfaces of the copper-nanocatalysts, it is evident that the Cu(211) coordination site possesses the highest activation energy relative to those of Cu(100) and Cu(111), hence, the reason for the noticeable high or low hydrogen yields. Thus, the potential of Cu giving high hydrogen yields from FA spans from the reactions of FA at the Cu(111) and Cu(100) sites.

Understanding the Deactivation Pathways of Iridium(III) Pyridine-Carboxiamide Catalysts for Formic Acid Dehydrogenation.

The degradation pathways of highly active [Cp*Ir(κ2 -N,N-R-pica)Cl] catalysts (pica=picolinamidate; 1 R=H, 2 R=Me) for formic acid (FA) dehydrogenation were investigated by NMR spectroscopy and DFT calculations. Under acidic conditions (1 equiv. of HNO3 ), 2 undergoes partial protonation of the amide moiety, inducing rapid κ2 -N,N to κ2 -N,O ligand isomerization. Consistently, DFT modeling on the simpler complex 1 showed that the κ2 -N,N key intermediate of FA dehydrogenation (INH ), bearing a N-protonated pica, can easily transform into the κ2 -N,O analogue (INH2 ; ΔG≠ ≈11 kcal mol-1 , ΔG ≈-5 kcal mol-1 ). Intramolecular hydrogen liberation from INH2 is predicted to be rather prohibitive (ΔG≠ ≈26 kcal mol-1 , ΔG≈23 kcal mol-1 ), indicating that FA dehydrogenation should involve mostly κ2 -N,N intermediates, at least at relatively high pH. Under FA dehydrogenation conditions, 2 was progressively consumed, and the vast majority of the Ir centers (58 %) were eventually found in the form of Cp*-complexes with a pyridine-amine ligand. This likely derived from hydrogenation of the pyridine-carboxiamide via a hemiaminal intermediate, which could also be detected. Clear evidence for ligand hydrogenation being the main degradation pathway also for 1 was obtained, as further confirmed by spectroscopic and catalytic tests on the independently synthesized degradation product 1 c. DFT calculations confirmed that this side reaction is kinetically and thermodynamically accessible.

Formic acid recovery from EDTA wastewater using coupled ozonation and flow-electrode capacitive deionization (Ozo/FCDI): Performance assessment at high cell voltage

Carbon resource recovery from toxic organic wastewater to reduce unnecessary energy loss and greenhouse gas emissions is rarely pursued. In the present study, a promising approach for formic acid (FA) recovery from EDTA wastewater was proposed by coupling ozonation and flow-electrode capacitive deionization (Ozo/FCDI). In the ozonation process, a FA productivity of 25% was obtained with the complete degradation of EDTA. The FA recovery from wastewater was compared under electrodialysis (i.e., without the use of flowable carbon electrodes, 0 wt%) and FCDI (i.e. using 5 wt% flowable carbon electrodes) processes and the results demonstrated the superiority of the FCDI process. After 390 min of operation, the accumulated FA concentration in the anode chamber of the FCDI system had increased to 633.6 mg/L with a low energy consumption of 8.0 kWh/kg FA, which was 1.8 times of the FA concentration in the electrodialysis (ED) process and nearly 6.4 times in the feed stream. These findings suggest the effective acquisition of high value-added FA in the Ozo/FCDI system; may provide new opportunities and challenges for the recovery of organic compounds.

Mineralization of formic acid from catalytic nitrate reduction effluent by UV-based and electrochemical processes

Abstract In this work, UV-based and electrochemical processes were proposed for formic acid (FA) mineralization, from an effluent generated on the nitrate catalytic reduction reaction. The results show that although direct photolysis (DP) does not have the ability to mineralize FA, heterogeneous photocatalysis (HP), photo-assisted electrochemical oxidation (PEO) and electrochemical oxidation (EO) have. In fact, it has been shown that FA mineralization is governed by the electrochemical process. When nitrate was added in the FA solution, all process exhibited an increase in FA mineralization, mainly for DP. For UV-based process, this fact can be linked to the nitrate photolysis generating hydroxyl radicals ( H O • ). On the other hand, the mineralization increase observed on the EO process, is associated with the increase in charge transfer, considering that the generation of oxidants is a rate-limiting-step, showing pseudo-zero-order constants for DP and HP, and pseudo-first-order for PEO and EO. The best results of FA mineralization with the smallest energy consumption was obtained by the electrochemical process. Besides, EO was not negatively influenced by the addition of nitrate.

Cobalt-Polypyrrole/Melamine-Derived Co-N@NC Catalysts for Efficient Base-Free Formic Acid Dehydrogenation and Formylation of Quinolines through Transfer Hydrogenation.

It is highly desired but remains a great challenge to develop non-noble metal heterogeneous catalysts to supersede noble metal catalysts for formic acid (FA) dehydrogenation and the corresponding transfer hydrogenation reactions. Herein, we developed a simple and feasible melamine-assisted pyrolysis strategy for the preparation of atomic cobalt-nitrogen (Co-N)-anchored mesoporous carbon with high metal loading (>6.8 wt %) and high specific surface area (750 m2 g-1). Systematic investigation reveals that both the organic carbon source polypyrrole and the nitrogen source melamine are crucial for the successful generation of such Co-N-based materials. The obtained samples (Co-N)n@NC were demonstrated to be highly efficient and robust catalysts for FA dehydrogenation and formylation of quinolines through transfer hydrogenation, exhibiting a very high hydrogen production rate of 16 451 mL·gCo-1·h-1 for FA dehydrogenation and affording excellent yields (up to 99%), selectivity (up to 98%), and stability for transfer hydrogenation. This work may provide a promising route for the fabrication of more low-cost metal-nitrogen catalysts for green fine chemical synthesis.

Influence of graphene and copper on the photocatalytic response of TiO2 nanotubes

The photocatalytic properties of TiO2 nanotubes (NTs) modified by copper nanoparticles (NPs) and (reduced) graphene oxide ((r)GO) are herein evaluated. The hybrid TiO2 nanomaterials were deeply characterized by means of N2 adsorption-desorption measurements, X-ray diffraction, X-ray photoelectron and UV–vis diffuse reflectance spectroscopies, and transmission electron microscopy. On Cu/TiO2 NTs, results show a stabilization of Cu NPs at a +I oxidation state due to a strong interaction with TiO2 NTs leading to an 80% increase in activity for formic acid (FA) degradation under UV irradiation. Contrary to GO/TiO2 NTs, in the presence of Cu, addition of non-reduced GO leads to a 150% increase in activity compared to its free counterpart Cu/TiO2 NTs while the use of partially reduced GO leads to a complete loss of any beneficial effect due to graphene oxide.

Polyol assisted formaldehyde reduction of bi-metallic Pt-Pd supported agro-waste derived carbon spheres as an efficient electrocatalyst for formic acid and ethylene glycol oxidation

This report explains, (i) the preparation of carbon spheres (CS) from agro-waste through hydrothermal carbonization (HTC) followed by high temperature carbonization, (ii) the decoration of bi-metallic Pt-Pd nanoparticles (Pt-Pd NPs) with different compositions (Pt/C, Pt0.5Pd1/C, Pt1Pd1/C and Pt1Pd0.5/C, Pd/C) on the carbon by ethylene glycol solvated polyol assisted formaldehyde reduction method and (iii) subsequently used as the electrocatalyst for formic acid (FA) and ethylene glycol (EG) electro-oxidation. The structural and morphological properties of the electrocatalysts were studied using advanced physicochemical characterization techniques. The obtained results well evidence the homogeneous dispersion of Pt-Pd NPs on the surface of the carbon. Especially, Pt0.5Pd1/C exhibited excellent electrocatalytic property towards formic acid electro-oxidation reaction (FAOR) with a higher current density (256 mA cm−2) and stability due to “third body effect”. On the other hand, Pt1Pd0.5/C expressed superior electrochemical performance towards ethylene glycol electro-oxidation reaction (EGOR) due to the strong interaction between high Pt content and Pd. Hence, this work reveals the improved electrocatalytic performance of bi-metallic Pt-Pd NPs supported biomass-derived carbon as a promising anodic electrocatalyst towards FAOR and EGOR.

Au/reduced graphene oxide composites: eco-friendly preparation method and catalytic applications for formic acid dehydrogenation

This paper presents a new, simple, accessible and environmentally friendly method to prepare gold-reduced graphene oxide composites (Au/rGO) with gold concentration of 2.5 wt%, 5 wt% and 10 wt%. The Au/rGO materials with low Au concentration present AuNPs of low dimensions and proved good catalytic activity for formic acid (FA) decomposition in aqueous solution. The most of the structural characteristics are not dependent of the gold content such as: large surface area (234–278 m2 g−1), good crystallinity of graphenes, few layers of carbon in the graphene support (5–6 layers), medium density of structural defects in graphene, the presence of remanent oxygenated groups on the graphene surface, very good dispersion of AuNPs on both sides of the graphene sheets. The AuNPs size instead is strongly dependent on the Au concentration: The smallest nanoparticles were obtained for Au2.5/rGO (3–5 nm) and the largest for Au10/rGO (10–14 nm). The position of the energy levels (conduction band and valence band) relative to the Fermi level also changes with the Au content.

A competent simultaneously co-electrodeposited Pt-MnOx nanocatalyst for enhanced formic acid electro-oxidation

Abstract In this paper, a new methodology replacing the typical sequential layer-by-layer immobilization, i.e., simultaneous co-electrodeposition protocol is proven eminent for assembling efficient binary nanoelectrocatalysts for formic acid (FA) electro-oxidation (FAO). This strategy is successful to integrate homogeneously Pt nanoparticles (nano-Pt; essential component for FA adsorption/oxidation) with manganese oxide nanowires (nano-MnOx; a CO poisoning alleviator) in a single blend avoiding the poisoning CO adsorption at the catalyst surface. The molar ratio of the catalyst's ingredients (Pt:Mn) in the deposition bath is critical in identifying the catalyst's composition of the prepared binary catalyst and thus, a molar ratio of (1:8) is optimum yielding the highest catalytic activity. It is believed that adjusting the catalyst's composition could preferably act against the adsorption of poisoning CO intermediate and/or providing an electronic support to the desired (low over potential) direct dehydrogenation pathway of FAO to CO2.

Synthesis Pd/biomass-based carbon microsheet composite for efficient dehydrogenation from formic acid

In present work, poplar catkin with microtube structure was carbonized at 800 °C in N2 and subsequently the carbonized microtubes were broken into microsheets by ultrasonic crushing. The palladium nanoparticles (NPs) were highly dispersed on the microsheets to form Pd/carbonized poplar catkin (Pd/CPC) composite. The synthesized composite showed extraordinary catalytic performance with high initial turnover frequency of 1613 molH2/(molmetal·h) for formic acid (FA) dehydrogenation. The composite also exhibited high selectivity, good stability and reproducibility during the catalytic process. These results indicate that Pd/CPC nanocatalyst has particular potential for hydrogenation reactions from hydrogen-rich substrates in practical applications.