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The reaction of carbon dioxide with hydroxide to form carbonate in near neutral or alkaline medium severely limits the energy and carbon efficiency of CO2 electroreduction. Here we show that by suppressing the otherwise predominant hydrogen evolution using alkali cations, efficient CO2 electroreduction can be conducted in acidic medium, overcoming the carbonate problem. The cation effects are general for three typical catalysts including carbon supported tin oxide, gold, and copper, leading to Faradaic efficiency of as high as 90% for formic acid and CO formation. Our analysis suggests hydrated alkali cations physisorbed on the cathode modify the distribution of electric field in the double layer, which impedes hydrogen evolution by suppress the migration of hydronium ions while at the same time promotes CO2 reduction by stabilizing key intermediates.

Atmospheric organic acids (OAs) are expected to enhance methanesulfonic acid (MSA)-driven new particle formation (NPF). However, the exact role of OAs in MSA-driven NPF remains unclear. Here, we employed a two-step strategy to probe the role of OAs in MSA–methylamine (MA) NPF. Initially, we evaluated the enhancing potential of 12 commonly detected OAs in ternary MA–MSA–OA cluster formation by considering the formation free energies of the (MSA)1(MA)1(OA)1 clusters and the atmospheric concentrations of the OAs. It was found that formic acid (ForA) has the highest potential to stabilize the MA–MSA clusters. The high enhancing potential of ForA results from its acidity, structural factors such as no intramolecular H bonds, and high atmospheric abundance. The second step is to extend the MSA–MA–ForA system to larger cluster sizes. The results indicate that ForA can indeed enhance MSA–MA NPF at atmospheric conditions (the upper limited temperature is 258.15 K), indicating that ForA might have an important role in MSA-driven NPF. The enhancing effect of ForA is mainly caused by an increased formation of the (MSA)2(MA)1 cluster, which is involved in the pathway of binary MSA–MA nucleation. Hence, our results indicate that OAs might be required to facilitate MSA-driven NPF in the atmosphere.

Background: Presently worldwide manufacturing of formic acid follows the permutation of methanol and carbon monoxide in presence of a strong base. But due to the use of toxic CO molecule and easy availability of CO2 molecule in the atmosphere, most of the research has been shifted from the conventional method of formic acid synthesis to direct hydrogenation of CO2 gas using different homogenous and heterogeneous catalysts. Objective: To develop reaction protocol to achieve easy CO2 hydrogenation to formic acid using Ionic liquid reaction medium. Methods: We used the sol-gel method followed by calcination (over 250oC for 5 hours) to synthesize two types of ruthenium metal-doped TiO2 nanoparticles (with and without ionic liquids), namely Ru@TiO2@IL and Ru@TiO2. We are reporting the application NR2 (R= CH3) containing imidazolium- based ionic liquids not only to achieve a good reaction rate but also to get agglomeration free ruthenium metal-doped TiO2 nanoparticles along with easy product isolation due to the presence of NR2 (R= CH3) functionality in ionic liquid structure. We synthesized various NR2 (R= CH3) functionalized ionic liquids such as 1-Butyl-3-methylimidazolium Chloride, 1,3-di(N,Ndimethylaminoethyl)- 2-methylimidazolium trifluoromethanesulfonate ([DAMI][TfO]), 1,3-di(N,Ndimethylaminoethyl)- 2-methylimidazolium bis (trifluoromethylsulfonyl) imide ([DAMI][NTf2]) and 1-butyl-3-methylimidazolium chloride ionic liquids which were synthesized as per the reported procedure. Results: We easily developed two types of Ru metal-doped TiO2 nanoparticles using the sol-gel method. After calcination, both Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) materials were characterized by XRD, FTIR, TEM, ICP-AES, EDS, and XANES analysis. After understanding the correct structural arrangement of Ru metal over TiO2 support, we utilized both Ru@TiO2@IL (3.2 wt% Ru) and Ru@TiO2 (1.7 wt% Ru) the materials as a catalyst for direct hydrogenation of CO2 in the presence of water and functionalized [DAMI] [TfO] ionic liquid. Conclusion: Here we demonstrated the preparation and characterization of TiO2 supported Ru nanoparticles with and without ionic liquid. After understanding the correct morphology and physiochemical analysis of Ru@TiO2@IL (3.2 wt% Ru), and Ru@TiO2 (1.7 wt% Ru) catalysts, we examined their application in CO2 reduction and formic acid synthesis. During the optimization, we also noticed the significant effect of functionalized [DAMI] [TfO] ionic liquid and water to improve the formic acid yield. Lastly, we also checked the stability of the catalyst by recycling the same till the 7th run.

Electrodeposited composite film electrodes prepared from electroplating baths with varying ratios of Ag+ and Sn2+ triflates were studied to understand how the performance of such materials varies a...

Honey bees are important managed pollinators that fulfill important ecological and economic functions. In recent decades, the obligate ectoparasite Varroa destructor severely affected the survival of honey bees, as it weakened them by different means. A common treatment against V. destructor is formic acid fumigation, which has been used for decades by beekeepers across the world. This treatment is known to be effective, but many beekeepers report adverse effects of formic acid on bees, which include damage to the brood, worker bee mortality, and queen loss. Little is known about the molecular mechanisms of formic acid detoxification in honey bees. Recently, we reported upregulation of the bee enzyme, 10-formyl-THFDH, under formic acid fumigation. Here, the active site of this enzyme is characterized by an interdisciplinary approach combining homology modeling and protein mutagenesis. In addition, the limitations of the 3D protein structure prediction program AlphaFold2 are shown in regard to docking studies. This study provides a more thorough understanding of the molecular detoxification mechanisms of formic acid in Apis mellifera.

A facile and environment-friendly atmospheric-pressure cold plasma treatment method was adopted to synthesize activated carbon supported bimetallic PdRu catalysts (PdRu/C–P) toward formic acid (FA) dehydrogenation. The results showed that the PdRu/C–P with a Pd/Ru mass ratio of 9/1 exhibited the highest activity featuring total gas volume of 337.2 ml during 4 h and initial turnover frequency (TOF) value of 954.2 h−1. In comparison with the PdRu/C-T catalyst prepared by thermal reduction, enhanced FA dehydrogenation activity of the PdRu/C–P catalysts could be mainly attributed to the efficient electron transfer from Ru to active Pd in the PdRu alloy, and the high PdRu/C atomic ratios arising from the migration of the PdRu active species from the pores to the outer surface of the support affected by Coulomb repulsion effect in the plasma. The total gas volume generated by FA over the PdRu/C–P was decreased to 88.4% and 86.5% after the second and third reaction cycles, respectively, in comparison with the first cycle. However, they have been decreased to 64.6% and 64.4%, respectively, for PdRu/C-T prepared by thermal reduction. In addition, the performance of the PdRu/C–P is a little inferior to PdAu/C–P prepared by cold plasma, but its catalytic stability is much better than the expensive PdAu/C–P. The enhancement of catalytic stability for the PdRu/C–P catalyst is attributed to the small and stable particle size of PdRu, and less leaching of active species resulting from the strong metal-support interaction induced by cold plasma.

Interconversion between CO2 + H2 and FA/formate is the most promising strategy for the fixation of carbon dioxide and reversible hydrogen storage; however, FA dehydrogenation and CO2 hydrogenation are usually studied separately using different catalysts for each reaction. This report describes of the catalysis of [Cp*Ir(N∧N)(X)]n+ (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl; X = Cl, n = 0; X = H2O, n = 1) bearing a proton-responsive N∧N pyridylpyrrole ligand for both reactions. Complex 2-H2O catalyzes FA dehydrogenation at 90 °C with a TOFmax of 45 900 h-1. Its catalysis is more active in aqueous solution than in neat solution under base-free conditions. These complexes also catalyze CO2 hydrogenation in the presence of base to formate under atmospheric pressure (CO2/H2 = 0.05 MPa/0.05 MPa) at 25 °C with a TOF value of 4.5 h-1 in aqueous solution and with a TOF value of 29 h-1 in a methanol/H2O mixture solvent. The possible mechanism is proposed by intermediate characterization and KIE experiments. The extraordinary activity of these complexes are mainly attributed to the metal-ligand cooperative effect of the the pyrrole group to accept a proton in the dehydrogenation of formic acid and assist cooperative heterolytic H-H bond cleavage in CO2 hydrogenation.

The purposes of this research were to synthesize single-atom 1 wt% Ni catalysts for the hydrogen production from formic acid using a simple impregnation of N-doped carbon with Ni acetate, to elucidate the nature of the Ni site using a combination of experimental methods with density functional theory calculations, to propose a reaction mechanism with this Ni site and to compare the catalytic properties of the single-atom catalysts with those of a traditional Ni catalyst with nanoparticles (3.9 nm). We found that the single Ni atom formed a Ni-N4 site in a double vacancy of curved N-doped graphene. Mass-based catalytic activities of the single-atom and traditional catalysts were close. The mechanism of the reaction involved the formation of formate through participation of the Ni and N atoms. The highest energy barrier (1.088 eV) was determined for the step of recombination of hydrogen atoms. This barrier corresponded well to the experimental apparent activation energy.

Converting CO2 emissions, powered by renewable electricity, to produce fuels and chemicals provides an elegant route towards a carbon-neutral energy cycle. Progress in the understanding and synthesis of Cu catalysts has spurred the explosive development of electrochemical CO2 reduction (CO2RR) technology to produce hydrocarbons and oxygenates; however, Cu, as the predominant catalyst, often exhibits limited selectivity and activity towards a specific product, leading to low productivity and substantial post-reaction purification. Here, we present a single-atom Pb-alloyed Cu catalyst (Pb1Cu) that can exclusively (~96% Faradaic efficiency) convert CO2 into formate with high activity in excess of 1 A cm–2. The Pb1Cu electrocatalyst converts CO2 into formate on the modulated Cu sites rather than on the isolated Pb. In situ spectroscopic evidence and theoretical calculations revealed that the activated Cu sites of the Pb1Cu catalyst regulate the first protonation step of the CO2RR and divert the CO2RR towards a HCOO* path rather than a COOH* path, thus thwarting the possibility of other products. We further showcase the continuous production of a pure formic acid solution at 100 mA cm–2 over 180 h using a solid electrolyte reactor and Pb1Cu. Alloying copper with isolated heteroatoms enables the C protonation of CO2 to HCOO* on activated copper sites, resulting in exclusive electrochemical CO2-to-HCOOH conversion with considerably high activity.

Carbon dioxide electrochemical reduction (eCO2RR) has been regarded as an important solution for low-carbon economy. However, challenges remain for searching low-cost and high selectivity catalysts. Here, we investigated electrocatalytic activity of molecular catalysts containing transition metal single atom supported on corrole as the eCO2RR catalysts (TM/SACC) by DFT. Various C1 products can be produced on the 14 TM/SACC, including methane (CH4), formic acid (HCOOH) and CO. We found CO and formic acid are major products on TM/SACC (TM = Ni, Pd, Zn, Cu, Au, Ag) at higher overpotentials, while methane are major eCO2RR products on TM/SACC (TM = Mn, Cr, Nb, Mo, Zr, V, Ti, Cd) at lower overpotentials. Our studies indicate Mn/SACC gives high selectivity for methane formation. Due to the lowest overpotential value of 0.46 V, Mn/SACC can be a quite promising catalyst with excellent performance for reduction of CO2 to methane along the most favorable pathway: CO2 → COOH∗ → CO∗ → CHO∗ → CH2O∗ → CH2OH∗ → CH3OH∗→CH3∗→CH4∗→CH4(g), among which the hydrogenation of CHO∗ to CH2O∗ and CH3OH∗ to CH3∗ and H2O are the limiting-potential step and rate-determining step, respectively. The study shows corrole with different transition metal could adjust the catalytic performance of electrocatalysts, which offer a hopeful strategy for the design of molecular catalysts.

Cold plasma has been proved to be an efficient method for synthesizing high performance Pd/C catalysts. However, the influence mechanism is still in obscure. In this work, the influence of cold plasma working gas, including air, Ar, O2 and H2, on the structure and performance of the Pd/C catalysts were investigated. Formic acid (HCOOH) dehydrogenation was selected as a probe reaction to investigate the performance of the Pd/C catalysts, and the catalytic activity of the catalysts follows the order: Pd/C-H2P > Pd/C-ArP > Pd/C-AirP ≈ Pd/C-O2P. The Pd/C-H2P catalyst possessed the highest activity, and the TOFinitial was as high as 552.4 h−1. The discharge parameters indicated that few micro discharge channels were generated in H2 plasma, and the power of a single-channel discharge is high. It facilitates the migration of the Pd active species from the pores to the outer surface of the support, and the mean size of the Pd nanoparticles were 2.6 ± 1.0 nm. In addition, the atomic ratio of Pd/C and the content of metallic Pd in Pd/C-H2P, determined by XPS, were as high as 0.0229 and 50.8%, respectively. These are beneficial to the reaction, and ensured the highest catalytic activity of the Pd/C-H2P catalyst. In contrast, the discharge in Ar plasma was mild and the regulation effect was not as strong as that in H2 plasma. Therefore, the catalytic activity of Pd/C-ArP was inferior to Pd/C-H2P. In addition, since there was a severe ablation of the carbon support and agglomeration of Pd nanoparticles in O2 plasma and air plasma, both of Pd/C-O2P and Pd/C-AirP exhibited poor catalytic activity toward HCOOH dehydrogenation.

Reactions of MH2 (M = Sr, Ba) with CO2 were explored in pure parahydrogen at 3.5 K using matrix isolation infrared spectroscopy and quantum chemical calculations. The formate complex HM(η2-O2CH) and formic acid complex (MH2)(HCOOH) were trapped and identified by isotopic substitutions and density functional theory (DFT) frequency calculations. Natural population analysis and the CO2 reduction mechanism demonstrate that hydride ion transfer from a metal hydride to a CO2 moiety facilitates the stabilization of such complexes.

The biodiesel industry produces around 10% w/w crude glycerol. This product has great potential to be valorized to obtain more valuable chemicals. Among all upgrading techniques of no-valuable crude glycerol, the electrochemical conversion is a promising technology. In this study, the green electrochemical conversion of glycerol into value-added products was investigated and optimized in a batch electro-catalytic reactor with a 450 ml working volume using platinum-based electrodes. The redox of glycerol in different solutions was studied by cyclic voltammetric study, the electrode behaviour was explored under chronopotentiometry/chronoamperometry conditions, the kinetics of glycerol consumption was investigated, and the electrode passivation/deactivation was studied by SEM (Scanning Electron Microscope), EDS (energy-dispersive X-ray spectroscopy), and regression models. The maximum non-acidic (dihydroxyacetone/hydroxyacetone or acetol/glycidol) and organic acids (acetic acid, lactic acid, formic acid) formations were optimized using response surface methodology (RSM). The effects of the treatment time, current intensity, type of anode electrode, pH and glycerol concentration were examined. Products concentrations and distributions, reaction mechanism and pathway were also investigated. The results showed that under strong acidic conditions (HCl; pH = 1.4), the highest solvent production (yield of 55%) was achieved using Pt electrode, at a current intensity of 0.31 A (5 mA/cm2).

The properties of a new catalytic Pt/N-graphene system in the gas-phase reaction of formic acid decomposition for the production of pure hydrogen were studied. Graphene powders undoped and doped with nitrogen atoms were used as carbon supports. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (TEM), and the chemisorption of CO were used to characterize the synthesized catalysts. It was found that the activity of the catalysts increased upon graphene doping with nitrogen atoms and with increasing the platinum concentration from 0.2 to 1 wt %; the catalyst selectivity in the test reaction was as high as 96–99%.

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.

Two novel porous zinc metal-organic frameworks (MOFs) 1 and 2 based on 1,1′-bis-((3,5-dicarboxybenzyl)-4,4′-bipyridinium) dichloride (H4bdcbpy·2Cl) ligand have been successfully synthesized by solvothermal reactions at different temperatures. Compounds 1 and 2 have the same composition but crystallize in different crystal systems. Compound 1 synthesized at low temperature crystallizes in the monoclinic system, and compound 2 prepared at high temperature crystallizes in the rhombohedral system. The structural differences of two compounds indicate that temperature plays an important role in the formation of the Zn-based MOFs. The Zn2+ ions are bridged by deprotonated formic acid moieties to form a 3D network in both compounds. H4bdcbpy·2Cl provided an acidic environment, which led to the decomposition of DMF into a rare C3H2N22+ cation. Nitrogen adsorption measurement displays that the adsorption capacity of 1 is 711 m2 g–1. The fluorescence spectra of compound 1 shows that there is a strong emission peak at 527 nm.

Formic acid oxidation (FAO) is a typical anode reaction in fuel cells that can be facilitated by modulating its direct and indirect reaction pathways. Herein, PtAu bimetallic nanoparticles loaded onto Co and N co-doping carbon nanoframes (CoNC NFs) were designed to improve the selectivity of the direct reaction pathway for efficient FAO. Based on these subtle nanomaterials, the influences of elemental composition and carbon-support materials on the two pathways of FAO were investigated in detail. The results of fuel cell tests verified that the appropriate amount of Au in PtAu/CoNC can promote a direct reaction pathway for FAO, which is crucial for enhancing the oxidation efficiency of formic acid. In particular, the obtained PtAu/CoNC with an optimal Pt/Au atomic ratio of 1:1 (PtAu/CoNC-3) manifests the best catalytic performance among the analogous obtained Pt-based electrocatalysts. The FAO mass activity of the PtAu/CoNC-3 sample reached 0.88 A·mgPt−1, which is 26.0 times higher than that of Pt/C. The results of first-principles calculation and CO stripping jointly demonstrate that the CO adsorption of PtAu/CoNC is considerably lower than that of Pt/CoNC and PtAu/C, which indicates that the synergistic effect of Pt, Au, and CoNC NFs is critical for the resistance of Pt to CO poisoning. This work is of great significance for a deeper understanding of the oxidation mechanism of formic acid and provides a feasible and promising strategy for enhancing the catalytic performance of the catalyst by improving the direct reaction pathway for FAO.

Most of the current electrocatalysts for the methanol oxidation reaction are precious group metals such as Pt, Pd, and Ru. However, their use is limited due to their high cost, scarcity, and issues with carbon monoxide poisoning. We developed a simple method to prepare a nickel foam (NF)-based monolith electrode with a NiO nanosheet array structure as an efficient electrocatalyst toward the oxidation of methanol to produce formate. By a simple ultrasonic acid treatment and air oxidation at room temperature, an inert NF was converted to NiO/NF as a catalytically active electrode due to the uniform NiO nanosheet array that was rapidly formed on the surface of NiO/NF. In alkaline electrolytes containing methanol, the as-prepared NiO/NF catalysts exhibited a lower methanol oxidation reaction (MOR) potential of +1.53 V vs RHE at 100 mA cm-2 compared to that of inert NF samples. The difference in potentials between the EMOR and the EOER at that current density was found to be 280 mV, indicating that methanol oxidation occurred at lower potentials as compared to the oxygen evolution reaction (OER). We also observed that the NiO/NF could also efficiently catalyze the oxidation of CO without being poisoned by it. NiO/NF retained close to 100% of its initial activity after 20,000 s of methanol oxidation tests at high current densities above 200 mA cm-2. Because of the simple synthesis method and the enhanced catalytic performance and stability of NiO/NF, this allows methanol to be used as an OER masking agent for the energy-efficient generation of value-added products such as formic acid and hydrogen.

Herein, an effective electrocatalyst exploiting non-noble metal oxide-containing of manganese oxide (MnO2) supported on graphitic carbon nitride (g-C3N4) for reduction of CO2 over a wide range of potential. The MnO2 decorated g-C3N4 nanocomposite was synthesized by precipitation, followed by calcination to attain uniform distribution of the MnO2. The MnO2 was found α-MnO2 crystal structure with a size of ∼0.5–2 nm having interlinear lattice spacing of 0.243 nm seen on the layer of g-C3N4 (50−100 nm). The high defective sites observed on MnO2/g-C3N4 (ID/IG) is 1.91 than pristine g-C3N4 (ID/IG) is 0.054. The core spectrum analysis of XPS showed N, C, O and Mn atoms in the as-synthesized composite. The electrocatalysts were executed for electrocatalytic hydrogenation of CO2 at lower onset potential of −0.14 V vs. RHE into C1 products having Faradaic efficiencies (FE) of 8, 47.45 and 65.28% at an applied potential of −0.14, −0.34 and −0.54 V vs. RHE, respectively. The catalyst has further used for the chemical hydrogenation of CO2, and the good yield of formic acid was 9603.28 μmol obtained. The enrichment of the electrocatalytic activities was observed due to the synergetic effect of both MnO2 and g-C3N4. This methodology will be applicable for industrial applications and it will help control environmental issues.

Prevention of runaway reactions is one of the ultimate goals of process safety engineering. However, the lack of knowledge for mechanism and kinetics of autocatalytic reactions enables to design safer processes handling reactive materials. The purpose of the present study was to accurately predict the induction period of autocatalytic reaction system composed by nitric acid and formic acid using a sophisticated kinetic model for the autocatalytic behavior. The reactions of nitric acid with organic compounds are autocatalytic and so can rapidly generate large amounts of heat and pressure without obvious warning signs. Thermal analyses were carried out using a reaction calorimeter while ion chromatography was employed to quantify reaction products. Exothermic reactions were observed to begin when the concentration of nitrous acid, which was identified as the autocatalyst, exceeded 4.6 ± 1.2 mmol L−1. A kinetic model was determined as d[HONO]/dt = 2.62 × 1012exp(1.06 × 104/T)･[HNO3]2.5±0.1[HCOOH]1.8±0.1[HONO]1.9±0.1. This model was in good agreement with other results obtained from reaction calorimetry.

In this study, we have reported a one-step synthesis of a TiO2@MoS2 heterostructure. TiO2@MoS2 was synthesized using a facile and cost-effective method. The as-synthesized TiO2@MoS2 heterostructure was characterized by suitable spectroscopic techniques. The obtained TiO2@MoS2 was utilized as a supercapacitor electrode material. Electrochemical studies show that the TiO2@MoS2 heterostructure possesses a specific capacitance of 337 F/g at a current density of 1 A/g in an aqueous solution. Furthermore, an application as a photocatalyst for the photoreduction of toxic hexavalent chromium was reported for the first time. This heterostructure showed the photoreduction of Cr6+ to Cr3+ in 120 min with formic acid as a scavenger under direct sunlight. A plausible mechanism of photoreduction of Cr6+ to Cr3+ under natural sunlight irradiation using TiO2@MoS2 is proposed.

Reactive organic fluid–mineral interactions at elevated temperatures contribute to the evolution of planetary matter. One of the less studied but important transformations in this regard involves t...

Electrochemical reduction of CO2 to chemicals and fuels is an interesting and attractive way to mitigate greenhouse gas emissions and energy shortages. In this work, we report the use of atomic In catalysts for CO2 electroreduction to CO. The atomic In catalysts were anchored on N-doped carbon (InA/NC) through pyrolysis of In-based metal-organic frameworks (MOFs) and dicyandiamide. It was discovered that InA/NC had outstanding performance for selective CO production in the mixed electrolyte of ionic liquid/MeCN. It is different from those common In-based materials, in which formate/formic acid is formed as the main product. The faradaic efficiency (FE) of CO and total current density were 97.2% and 39.4 mA cm-2, respectively, with a turnover frequency (TOF) of ∼40 000 h-1. It is one of the highest TOF for CO production to date for all of the catalysts reported. In addition, the catalyst had remarkable stability. Detailed study indicated that InA/NC had higher double-layer capacitance, larger CO2 adsorption capacity, and lower interfacial charge transfer resistance, leading to high activity for CO2 reduction. Control experiments and theoretical calculations showed that the In-N site of InA/NC is not only beneficial for dissociation of COOH* to form CO but also hinders formate formation, leading to high selectivity toward CO instead of formate.

Enhanced oxidation of formic acid (FAO) is observed at NiOx/Pd/GC anodes in the presence of urea as a blending fuel. FAO is noticeably enhanced (in the presence of urea as a blending fuel) as demonstrated by CV measurements where a five-fold increase of the direct FAO peak (Ipd), and a favorable negative shift of its onset potential (Eonset) are observed. Additionally, a six-fold increase of the fuel utilization (FU), expressed in the amount of charge consumed during FAO is markedly enhanced in FA-urea fuel blend (0.3 M FA and 0.2 M urea) compared to that obtained in the absence of urea (i.e., 0.3 M FA only) at the NiOx/Pd/GC electrode. Additionally, capacitance measurements of the electrode/electrolyte interface increases in line with FAO activity. Urea molecules are thought to form a bridged H-bonding with formate anions thus facilitating a favorable adsorption geometry allowing for a facile C–H scissoring, thus promoting the oxidative dehydrogenation pathway of FA to CO2. A plausible explanation assumes the formation of 6- and/or 8-membered rings between formate anion and urea (via hydrogen bonding). These findings emphasize the importance of the proper design of the catalyst together with the smart selection of the blending fuel with FA.

The electrochemical reduction of CO2 (ERC) to valuable chemicals has attracted extensive attention. However, the relatively low selectivity and efficiency of the reaction remain challenges. In this study, Cu electrodes derived from Cu2 O with predominant (111) facets are synthesized by cetyltrimethylammonium bromide-assisted preparation. The optimized electrode shows a high faradaic efficiency of 90 % for HCOOH obtained by ERC at -2.0 V (vs.SCE), which surpasses most reported Cu electrodes. Based on a comprehensive analysis of the relationship between the catalytic activity and the thickness of the Cu2 O layer, the catalytic activity of the unit active site on the Cu2 O-derived Cu electrodes is found to be higher than that on the blank Cu electrode. DFT calculations indicate that OCHO* would be produced preferentially over *COOH in the presence of cetyltrimethylammonium bromide (CTAB). This deduction is verified by testing of the effects of CTAB and KBr addition on HCOO- selectivity.

We demonstrate the ability of tetraalkylammonium borohydrides to capture large amounts of CO2 , even at low CO2 concentrations, and reduce it to formate under ambient conditions. These materials show CO2 absorption capacities up to 30 mmol CO 2 g-1 at room temperature and 1 bar CO2 . Every BH4 - anion can react with three CO2 molecules to form triformatoborohydride ([HB(OCHO)3 ]- ). The thermodynamics and kinetics of the reaction were monitored by a magnetic suspension balance (MSB). Direct CO2 capture and reduction from air was achieved with tetraethyl, -propyl, and -butylammonium borohydride. The alkyl chain length played an important role in the kinetics and thermodynamics of the reaction, especially in CO2 diffusivity (crystallinity and free-volume), activation energy (charge-transfer dependent on the alkyl chain), and hydrophobicity. Adding HCl gave formic acid and the corresponding chloride ammonium salt, which can be recycled. In addition, transfer of formate was achieved for the N-formylation of an amine.

There is an increasingly interest in the use of small organic molecules in the interconversion between chemical and electrical energies. Among the strategies to improve the processes of yielding electrical energy in fuel cells and the production of clear hydrogen in electrochemical reform is the use of kinetic instabilities to improve the conversion and selectivity. Herein we report on the electrocatalytic efficiency of the oxidation of ethylene glycol, glycerol, and glucose, under regular and oscillatory regimes, on polycrystalline platinum, in sulfuric acid aqueous solution, and at 25 oC. Despite the high overpotentials for the electro-oxidation of these molecules, the electrochemical activity along quasi-stationary potentio/gavanostatic experiments evidenced that, in all cases, relatively lower potential values, and thus higher activity, are reached during oscillations. Noticeably higher power densities for the electrooxidation of ethylene glycol and glycerol under oscillatory regime in a hypothetical direct liquid fuel cell. The use of identical experimental conditions of that of our previous study[J. Phys. Chem. C 120 (2016) 22365] allowed at discussing some universal trends for seven small organic molecules. We compile the results in terms of the peak current, the maximum poisoning rate found along the oscillations, and the oscillation frequency. The three parameters were found to decrease in the order: formaldehyde > formic acid > methanol > ethanol > ethylene glycol > glycerol > glucose. In addition, we discussed the increase of the voltammetric current with the self-organized poisoning rate and reinforce the trend that high electrocatalytic activity implies high susceptibility to surface poisoning for this set of species. Finally, the analysis done for all species (formic acid, formaldehyde, methanol, ethylene glycol, ethanol, glycerol, and glucose) adds to the available thermodynamic data and is a benchmark against which the activities under oscillatory regime at 25 oC may be compared or assessed. This point of reference permits to explore further experimental conditions that are relevant for energy-related devices, including the conversion of chemical into electrical energy and the electrochemical reform to produce clean hydrogen in electrolyzers.

CO2 hydrogenation over Ni/SiO2 catalysts with and without Na additives was investigated in terms of the catalytic activity, selectivity of CO2 methanation and reaction mechanism. Na additives could cause the formation of Na2O species that might deposit on the Ni surface of Ni/SiO2 (NiNax/SiO2). When the Ni metal is partially covered with Na2O species, a highly positive charge on the Ni metal could occur compared to the original Ni/SiO2 catalyst. The addition of Na to the Ni/SiO2 catalyst could influence selectivity toward CO formation. The adsorbed formic acid is the major intermediate on the Ni/SiO2 catalyst during CO2 hydrogenation. The formic acid species might decompose into adsorbed CO complexes in the forms of linear CO, bridged CO and multibonded CO. CH4 formation should be ascribed to the hydrogenation of these adsorbed CO complexes. The Ni/SiO2 catalyst with the Na additive might have very weak ability for H2 and CO adsorption, thus making it difficult for CO methanation to occur. The hydrogen carbonate species adsorbed on the NiNax/SiO2 catalysts were proposed to be the key intermediate, and they might decompose to CO or be hydrogenated to form CH4.

Formic acid is a liquid organic hydrogen carrier. Metal and metal-complex catalysts are known to catalyze the hydrogen production from formic acid and hydrogen transfer reactions with formic acid a...

We report herein a series of Cp*Ir complexes containing a rigid 8-aminoquinolinesulfonamide moiety as highly efficient catalysts for the dehydrogenation of formic acid (FA). The complex [Cp*Ir(L)Cl] (HL = N-(quinolin-8-yl)benzenesulfonamide) displayed a high turnover frequency (TOF) of 2.97 × 104 h-1 and a good stability (>100 h) at 60 °C. Comparative studies of [Cp*Ir(L)Cl] with the rigid ligand and [Cp*Ir(L')Cl] (HL' = N-propylpypridine-2-sulfonamide) without the rigid aminoquinoline moiety demonstrated that the 8-aminoquinoline moiety could dramatically enhance the stability of the catalyst. The electron-donating ability of the N,N'-chelating ligand was tuned by functionalizing the phenyl group of the L ligand with OMe, Cl, and CF3 to have a systematical perturbation of the electronic structure of [Cp*Ir(L)Cl]. Experimental kinetic studies and density functional theory (DFT) calculations on this series of Cp*Ir complexes revealed that (i) the electron-donating groups enhance the hydrogen formation step while slowing down the β-hydride elimination and (ii) the electron-withdrawing groups display the opposite effect on these reaction steps, which in turn leads to lower optimum pH for catalytic activity compared to the electron-donating groups.

Nowadays, the self-accelerating increase in global temperatures strengthens the idea that the cutting of CO2 emissions will not be enough to avoid climate change, thus CO2 from the atmosphere must be removed. This gas can be easily trapped by converting it to bicarbonate using hydroxide solutions. However, bicarbonate must be converted into a more valuable product to make this technology profitable. Several studies show great efficiency when reducing bicarbonate solutions saturated with pure CO2 gas to formate. However, those approaches don’t have a real application and our objective was to obtain similar results without pure CO2 saturation. The method consists of electroreduction of the bicarbonate solution using bulk tin (Sn) as catalysts. Tin is a relatively cheap material that, according to previous studies performed in saturated bicarbonate solutions, shows a great selectivity towards formate. The 1H NMR analysis of bicarbonate solutions after electroreduction show that, without pure CO2 gas, the faradic efficiency is around 18% but almost 50% for saturated ones. The formate obtained could be used to power formate/formic acid fuel cells obtaining a battery-like system, with greater energy density than common lithium batteries, but electroreduction efficiency needs to be improved to make them competitive.

We report a novel approach toward the catalytic hydrogenation of CO2 to methanol performed in the gas-solid phase using multinuclear iridium complexes at low temperature (30-80 °C). Although homogeneous CO2 hydrogenation in water catalyzed by amide-based iridium catalysts provided only a negligible amount of methanol, the combination of a multinuclear catalyst and gas-solid phase reaction conditions led to the effective production of methanol from CO2. The catalytic activities of the multinuclear catalyst were dependent on the relative configuration of each active species. Conveniently, methanol obtained from the gas phase could be easily isolated from the catalyst without contamination with CO, CH4, or formic acid (FA). The catalyst can be recycled in a batchwise manner via gas release and filling. A final turnover number of 113 was obtained upon reusing the catalyst at 60 °C and 4 MPa of H2/CO2 (3:1). The high reactivity of this system has been attributed to hydride complex formation upon exposure to H2 gas, suppression of the liberation of FA under gas-solid phase reaction conditions, and intramolecular multiple hydride transfer to CO2 by the multinuclear catalyst.

Promoting formic acid electrochemical oxidation through the dehydrogenation path is critical for the development of direct liquid fuel cells. Herein, we report the modification of intermetallic PtBi hexagonal nanoplates by depositing trace amounts of Pd atoms (PtBi@1.8% Pd HNPs) to obviously improve the selectivity of the dehydrogenation path instead of the dehydration path, achieving highly efficient formic acid electrocatalysis. Impressively, PtBi@1.8% Pd exhibits superior mass activity of 4.17 A mgPt+Pd−1, which is 27 and 9.6 times higher than that of commercial Pt/C and Pd black catalysts, respectively. During chronoamperometry measurements, PtBi@1.8% Pd maintains much higher mass activity than the benchmark catalysts. The excellent electrocatalytic performances are attributed to the synergetic effect between the tensile-strained/electronic-modified Pd and the electronic-modified intermetallic PtBi, providing a novel co-modification strategy to boost electrocatalysis.

Kinetic studies have been carried out for the base-free hydrogenation of CO2 to formic acid using a heterogeneous ruthenium-inserted hydrotalcite (Ru-HT) catalyst. An impressive turnover number (TON = 11 389) was achieved for formic acid under the optimized reaction conditions using a methanol : water mixture as the solvent (5 : 1, v/v) with 60 bar total pressure at 60 °C for 24 hours. The rates were determined directly in terms of the formation of formic acid with time. Kinetics were performed by carrying out experiments concerning the amount of catalyst, the individual partial pressures of CO2 and H2, the total pressure, temperature, agitation speed, reaction volume and v/v ratio of the mixed solvent. The rate of formic acid formation was first order on the amount of catalyst and partial pressures of CO2 and H2. The best reaction conditions achieved from the kinetic parametric optimization were: 100 mg catalyst, 30 bar pCO2, 30 bar pH2, 60 °C temperature, 800 rpm agitation speed and methanol–water (5 : 1, v/v) solvent. The computed activation parameters obtained from the temperature-dependent rate of formic acid formation were Ea = 34.5 ± 2.5 kJ mol−1, ΔH# = 32 ± 2.5 kJ mol−1 and ΔS# = −384 ± 5 J deg−1 mol−1. The presence of water in the mixed solvent effectively enhanced the reaction rate, which is characteristically observed due to its molecular effect. Two mechanistic routes for CO2 hydrogenation to formic acid are proposed and discussed based on the kinetic and experimental observations. The studied parameters were found to be significantly effective to increase the rate of reaction appreciably.

Direct reduction of bicarbonate, a typical product of CO2 captured in alkaline solution, into value-added organics is one promising way to achieve a simplified and green CO2 capture and utilization process. In this work, a new strategy of bicarbonate reduction coupled with methanol oxidation into a dual formation of formate under mild hydrothermal conditions is reported. A 68% formate production efficiency based on the reductant methanol and nearly 100% selectivity of formate were obtained via a Pd0.5Cu0.5/C catalyst at 180 °C. An operando hydrothermal ATR-FTIR study proved that the bicarbonate was reduced by the in situ generated hydrogen from methanol, which was stepwise oxidized to formaldehyde and formic acid. Notably, DFT calculations and a qNMR study of the 13C and 2H (D) isotopic labelling revealed that H2O molecules not only supplied the hydrogen for bicarbonate reduction but also acted as an indispensable promoter to enhance the catalytic performance of Pd0.5Cu0.5/C for methanol activation.

We fabricated a CO2 electrolyzer in order to investigate the energy requirements and the electrical-to-chemical energy conversion efficiency obtained when using boron-doped diamond as the cathode. The main product in the electrochemical reduction of CO2 using a boron-doped diamond electrode is formic acid, with a faradaic efficiency of 96%. The electrical-to-chemical energy conversion efficiency was investigated at various bias voltages, and it reached 43%, very close to the predicted maximum value, at a cell voltage of 3 V. If the secondary products, hydrogen and carbon monoxide, are also considered, the total electrical-to-chemical energy conversion efficiency was as much as 45%.

The metal organic frameworks (MOFs) supported Pd catalysts for H2 generation from formic acid (FA) were synthesized in this work, via a facile excessive impregnation-low temperature reduction approach. Among the synthetic catalysts, 10% Pd/MOF-Cr (18) displayed a remarkable performance for catalyzing FA dehydrogenation in additive-free aqueous solution, and the corresponding TOFmid achieved 537.8 h−1 at 323 K. Furthermore, the bimetallic Ni–Pd alloy catalysts were prepared by the introduction of Ni in the subsequent work. Fortunately, 10% Ni0.4Pd0.6/MOF-Cr was found to be a highly active and fairly durable catalyst, exhibiting a TOFmid as high as 737.9 h−1 at 323 K with almost 100% XFA (final) and SH2, and remained 94% of its original activity in the third cyclic catalysis. Meanwhile, Ni was discovered to be indispensable in increasing the electron density of Pd, downsizing the immobilized metal particles and inhibiting the agglomeration of the loaded nanoparticles.

Recently, nitrate as one of the water pollutants has caused widespread concerns. The nitrite and ammonium of nitrate reduction products have also been regarded as contaminants. Thus, increasing the nitrate removal rate and improving the nitrogen selectivity simultaneously have attracted the attention of researchers. To remove the nitrate with high nitrogen selectivity from an aqueous solution, 2D g-C3N4 was intercalated into 3D TiO2/Ti3C2 to fabricate the TiO2/Ti3C2/g-C3N4 photocatalyst with 3D/2D ternary heterojunctions. 0.5 TiO2/Ti3C2/g-C3N4 photocatalyst exhibited the highest nitrate conversion and nitrogen selectivity, which reached 93.03% nitrate conversion and 96.62% nitrogen selectivity after 40 min of irradiation. Moreover, its photocatalytic performance remained stable after 5 cycles. It was observed that the high concentration of nitrite was advantageous for improving the nitrogen selectivity. In TiO2/Ti3C2/g-C3N4 composites, 3D Ti3C2 served not only as a template for preparing 2D g-C3N4, but also as a channel for the electron transfer between TiO2 and g-C3N4. Photogenerated electrons in the conduction band of TiO2 migrated to the valence band of g-C3N4 through Ti3C2. The corresponding holes remained on the valence band of TiO2 and were captured by formic acid in an aqueous solution to generate reducing COO˙−. Then, COO˙− in the solution and photoinduced electrons in the conduction band of g-C3N4 reduced nitrate to nontoxic and harmless nitrogen with high selectivity. Finally, the Z-scheme heterojunction was proposed over 0.5 TiO2/Ti3C2/g-C3N4 photocatalyst on working for the photocatalytic nitrate reduction in water.

In this article solvothermally synthesized copper selenide nanostructures have been reported as highly efficient electrocatalysts for carbon dioxide reduction under ambient conditions with high selectivity for carbon-rich C2 products at a low applied potential. In addition to electrochemical measurements, density functional theory calculations were also performed to investigate the adsorption energy of the key intermediate carbon monoxide on the catalyst surface. The authors proposed that CO adsorption energy on the surface can be a critical component to determine the extent of CO2 reduction on the surface, whereby a low CO adsorption energy was expected to yield primarily C1 products while a very large adsorption energy leads to catalyst poisoning. In this article the authors have shown that by carefully designing the catalyst surface to optimize the CO adsorption energy and dwell time, selenide based electrocatalysts can indeed show more efficient CO2 reduction compared to the base metal, leading to carbon-rich products. This is one of the first reports where the Cu2Se surface has been studied in detail with experimental as well as DFT studies for CO2 reduction. Interestingly, the reduction products showed dependence on the applied potential forming exclusively formic acid at a high applied potential (1.2 V and higher vs. RHE), while ethanol and acetic acid were produced in high yield at potentials lower than 0.8 V vs. RHE. The applied potential required for CO2 with copper selenide was as low as 100 mV vs. RHE and is one of the lowest reported to date. The CO2 reduction products were analyzed through NMR and GC TCD spectroscopy which showed ethanol and acetic acid production in excess of 80% faradaic efficiency at a low applied potential.

A simple and efficient protocol for the formylation of amines with formic acid, catalyzed by a polyoxometalate-based chromium catalyst, is described. Notably, this method shows excellent activity and chemoselectivity for the formylation of primary amines; diamines have also been successfully employed. Importantly, the chromium catalyst is potentially non-toxic, environmentally benign and safer than the widely used high valence chromium catalysts such as CrO3 and K2Cr2O7. The catalyst can be recycled several times with a negligible impact on activity. Finally, a plausible mechanism is provided based on the observation of intermediate and control experiments.