Selective Dehydrogenation Of Formic Acid Research Articles

Selective Dehydrogenation of Formic Acid Catalyzed by Air‐Stable Cuboidal PN Molybdenum Sulfide Clusters

AbstractFormic acid is considered as a promising hydrogen storage material in the context of a green hydrogen economy. In this work, we present a series of aminophosphino and imidazolylamino Mo3S4 cuboidal clusters which are active and selective for formic acid dehydrogenation (FAD). Best results are obtained with the new [Mo3S4Cl3(ediprp)3](BPh4) (4(BPh4)) (ediprp=(2‐(diisopropylphosphino)ethylamine)) cluster, which is prepared through a simple ligand exchange process from the Mo3S4Cl4(PPh3)3(H2O)2 precursor. Under the conditions investigated, complex 4+ showed significantly improved performance (TOF=4048 h−1 and 3743 h−1 at 120 °C in propylene carbonate using N,N‐dimethyloctylamine as base after 10 min and 15 min, respectively) compared to the other reported molybdenum compounds. Mechanistic investigations based on stoichiometric and catalytic experiments show that cluster 4+ reacts with formic acid in the presence of a base to form formate substituted species [Mo3S4Cl3‐x(OCOH)x(ediprp)3]+ (x=1–3) from which the catalytic cycle starts. Subsequently, formate decarboxylation of the partially substituted [Mo3S4Cl3‐x(OCOH)x(ediprp)3]+ (x=1, 2, 3) catalyst through a β‐hydride transfer to the metal generates the trinuclear Mo3S4 cluster hydride. Dehydrogenation takes place through protonation by HCOOH to form Mo−H⋅⋅⋅HCOOH dihydrogen adducts, with regeneration of the Mo3S4 formate cluster. This proposal has been validated by DFT calculations.

Modification of Pd Nanoparticles with Lower Work Function Elements for Enhanced Formic Acid Dehydrogenation and Trichloroethylene Dechlorination.

Catalytic degradation of halogenated contaminants by palladium (Pd) is a promising technology for environmental remediation. However, the low utilization of H by Pd catalyst and its easy poisoning prevent its applications. Here, low work function elements (B or Ag) were incorporated into Fe@C-supported Pd nanoparticles (NPs) to alter their crystalline structure and induce electronic effects, addressing these issues. The Pd mass-normalized dechlorination rates of trichloroethylene (TCE) by Fe@C-Pd-B and Fe@C-Pd-Ag were 51 and 59 times higher than that of unmodified Fe@C-Pd, respectively. The H utilization efficiency of Fe@C-Pd-B and Fe@C-Pd-Ag was 5.4 and 7.2 times higher than that of unmodified Fe@C-Pd, respectively. Various characterizations suggest that the B or Ag incorporation induced the charge redistribution and elevated the electron density of Pd atoms, resulting in the enhanced formic acid (FA) dehydrogenation and TCE dechlorination. Although the Ag incorporation presented a relatively higher H utilization due to the suppressed combination of H and accumulation of unsaturated hydrocarbons (i.e., C2H4), the Fe@C-Pd-Ag was easily deactivated. In contrast, the B incorporation enabled the Pd NPs with a good stability. These findings can guide the rational design of robust Pd-based catalysts for efficient and selective FA dehydrogenation and chlorinated contaminant degradation.

In-situ nitrogen and Cr2O3 co-doped MOF-derived porous carbon supported palladium nanoparticles: A highly effective catalyst towards formic acid dehydrogenation

Fast and high selective dehydrogenation of formic acid (FA) is regarded as one of the most promising pathways to obtain the clean energy carrier: hydrogen. In this work, a nitrogen and Cr2O3 co-doped hierarchical carbon material has been successfully synthesized by in-situ pyrolysis of NH2-MIL-101(Cr) in one step, followed by boiling in hot NaOH solution for surface etching. The activated carbon material is used to anchor the ultrafine Pd nanoparticles (2.18 nm) for formic acid dehydrogenation (FAD). As a result, the 5 wt% Pd@Cr2O3-NPCB-850 exhibits an excellent catalytic activity towards FAD: the turnover frequency (TOF) value is as high as 11 241 h−1 at 333 K, and the selectivity of H2 is up to 100%. The excellent catalytic performance is mainly attributed to the existence of N species and Cr2O3, which plays an important role of electron transfer and anti-aggregation. Our studies open a new methodology for convenient and fast syntheses of nitrogen and metal oxide co-doped activated carbon material, which also provides potential access for producing more highly effective catalysts for other catalytic reactions.

Controllable Synthesis of Supported PdAu Nanoclusters and Their Electronic Structure-Dependent Catalytic Activity in Selective Dehydrogenation of Formic Acid.

We report the design and synthesis of uniform PdAu alloy nanoclusters immobilized on diamine and graphene oxide-functionalized silica nanospheres. The structure-dependent activity for selectively catalytic dehydrogenation of formic acid (FA) has been evaluated and optimized by controlling the Pd/Au mole ratio and the carrier components. The relationship between the catalyst structure and activity has been investigated via both experiments and characterization. High-resolution transmission electron microscopy (TEM) and X-ray diffraction (XRD) proved the formation of PdAu alloy nanoclusters. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS) analyses verified the electron transfer between Au, Pd, and the support. An outstanding turnover frequency (TOF) value of 16 647 h-1 at 323 K, which is among the highest activity for FA dehydrogenation ever reported, can be achieved at optimized conditions and ascribed to the combination of the bimetallic synergistic effect and the carrier effect.

Immobilization of palladium silver nanoparticles on NH2-functional metal-organic framework for fast dehydrogenation of formic acid

Selective dehydrogenation of formic acid is regarded as a universal strategy for providing a clean energy carrier (hydrogen, H2) to reduce the dependence on fossil fuel. In this work, ultrafine PdAg nanoparticles (NPs) are successfully immobilized on NH2-functionalized metal–organic framework MIL-101(Cr) by a facile wet-reduction method. By virtue of amine group, the size of obtained PdAg NPs can be controlled into 2.2 nm, which are monodispersed on NH2-MIL-101(Cr) surface. In addition, the resulting Pd0.8Ag0.2 NPs/NH2-MIL-101(Cr) catalyst systems demonstrate excellent catalytic activity for formic acid decomposition in mild condition, the turn over frequency (TOF) value can achieve as high as 1475 h−1 at 323 K, which is comparable to most of the reported noble metal heterogeneous catalysts for this catalytic reaction under similar conditions. The excellent catalytic kinetics is mainly attributed to the ultrafine size and high dispersion of PdAg NPs. Also, the amine group from NH2-MIL-101(Cr) support facilitates the OH bond dissociation of formic acid and improves the kinetics of formic acid decomposition.

One-step synthesis of Ni@Pd/NH2-Fe3O4 nanoparticles as affordable catalyst for formic acid dehydrogenation

Currently, one of the critical issues in the world is finding an appropriate green alternative to fossil fuels due to the concerns about global warming. As a hydrogen source, formic acid has been given particular attention owing to the attractive features such as high-energy density, no toxicity, high stability at ambient temperature and high hydrogen content. Introducing an affordable and highly efficient catalyst with easy recovery from the reaction mixture for selective dehydrogenation of formic acid is still demanding. In this report, we used a simple one-step process to synthesize Ni@Pd core shell nanoparticles on 3-aminopropyltriethoxysilane modified Fe 3 O 4 nanoparticles. The existence of Ni and Pd results in a synergic effect on the catalytic activity. The NH 2 groups play an important role for obtaining well-dispersed ultrafine particles with high surface area and active sites. In addition, Fe 3 O 4 lead to convenient magnetic recovery of the catalyst from reaction mixture. Our results indicate that the as-prepared catalyst give the superb turnover frequency of 5367.8 h −1 with no additive, which is higher than most of the previously reported catalysts.

Anchoring Pd-nanoparticles on dithiocarbamate- functionalized SBA-15 for hydrogen generation from formic acid

Hydrogen (H2) generation from natural biological metabolic products has remained a huge challenge for the energy arena. However, designing a catalytic system with complementary properties including high surface area, high loading, and easy separation offers a promising route for efficient utilization of nanoreactors for prospective H2 suppliers to a fuel cell. Herein, selective dehydrogenation of formic acid (FA) as a natural biological metabolic product to H2 and CO2 gas mixtures has been studied by supporting ultrafine palladium nanoparticles on organosulfur-functionalized SBA-15 nanoreactor under ultrasonic irradiation. The effects of the porous structure as a nanoreactor, and organosulfur groups, which presented around the Pd due to their prominent roles in anchoring and stabilizing of Pd NPs, studied as a superior catalyst for selective dehydrogenation of FA. Whole catalytic systems were utilized in ultrasonic irradiation in the absence of additives to provide excellent TOF/TON values. It was found that propose catalyst is a greener, recyclable, and more suitable option for the large-scale application and provide some new insights into stabilization of ultra-fine metal nanoparticle for a variety of applications.

Cobalt Single-Atom Catalysts with High Stability for Selective Dehydrogenation of Formic Acid.

Metal–organic framework (MOF)‐derived Co‐N‐C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co‐N‐C catalyst achieves superior activity, better acid resistance, and improved long‐term stability compared with nanoparticles synthesized by a similar route. High‐angle annular dark‐field–scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and X‐ray absorption fine structure characterizations reveal the formation of CoIINx centers as active sites. The optimal low‐cost catalyst is a promising candidate for liquid H2 generation.

Cobalt Single‐Atom Catalysts with High Stability for Selective Dehydrogenation of Formic Acid

AbstractMetal–organic framework (MOF)‐derived Co‐N‐C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co‐N‐C catalyst achieves superior activity, better acid resistance, and improved long‐term stability compared with nanoparticles synthesized by a similar route. High‐angle annular dark‐field–scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and X‐ray absorption fine structure characterizations reveal the formation of CoIINx centers as active sites. The optimal low‐cost catalyst is a promising candidate for liquid H2 generation.

Crafting Porous Carbon for Immobilizing Pd Nanoparticles with Enhanced Catalytic Activity for Formic Acid Dehydrogenation

AbstractThe development of highly active heterogeneous catalytic systems that catalyze formic acid (FA) to generate CO‐free H2 holds great promise for future energy demands, but is often limited by the low catalytic activity and stability of metal catalysts under ambient conditions. It is thus highly desirable to rationally design a catalyst to boost the catalytic performance. Herein, a general room‐temperature HNO3‐treatment approach (RTHTA) is developed to accomplish surface modification of various porous carbon materials for immobilizing ultrafine palladium nanoparticles (Pd NPs). A significantly enhanced catalytic performance of the immobilized Pd NPs toward the selective dehydrogenation of FA is achieved, which gives a record‐high turnover frequency of 13333 h−1 at 60 °C, corresponding to a calculated H2 generation rate of 50.8 L H2 min−1 gPd−1. The results presented here may provide insight into the formation and stabilization of highly active immobilized metal nanoparticles, as well as the enhanced catalytic performance of Pd NPs for catalytic dehydrogenation reactions.

Ligand Design for Catalytic Dehydrogenation of Formic Acid to Produce High-pressure Hydrogen Gas under Base-free Conditions.

A series of Cp*Ir (Cp* = pentamethylcyclopentadienyl anion) complexes with amino-functionalized ligands were developed for the production of high-pressure H2 via catalytic dehydrogenation of formic acid (DFA) in water under base-free conditions. The Ir complexes with 2,2'-bipyridine (bpy) ligands bearing amino or alkylamino groups at the para positions exhibited high activity and stability for DFA compared with complexes containing bpy ligands bearing para-hydroxyl groups. In addition, para-amino groups afforded superior catalytic stability under high-pressure conditions compared with ortho-amino groups. By exploiting these amino-functionalized Cp*Ir complexes, it was possible to continuously produce high-pressure CO-free H2 via selective DFA in water upon the addition of concentrated FA (>99.5 wt %) to the base-free solution. Systematic investigation of the ligand effects on DFA revealed that the presence of alkylamino groups on the bpy ligand enhanced the catalytic activity (initial turnover frequency, TOF), although the stability decreased with increasing alkyl chain length on the amino groups. According to a Hammett plot, the increased catalytic activity of the Ir complexes after the introduction of amino-functionalized ligands may be attributable to the electron-donating effect of para-amino groups on the bpy ligand. Based on the experimental results, a reaction mechanism is proposed that involves a hydride intermediate whose stability is affected by the position of the amino groups on the bpy ligand, as confirmed through NMR studies.

Selective formic acid dehydrogenation at low temperature over a RuO2/COF pre-catalyst synthesized on the gram scale

Selective formic acid dehydrogenation over an efficient RuO2/COF pre-catalyst with good dispersion of the active metal and large N-content on the COF support.

Solvent effects on high-pressure hydrogen gas generation by dehydrogenation of formic acid using ruthenium complexes

High-pressure H2 was produced by the selective dehydrogenation of formic acid (DFA) using ruthenium complexes at mild temperatures in various organic solvents and water. Among the solvents studied, 1,4-dioxane was the best candidate for this reaction to generate high gas pressure of 20 MPa at 80 °C using the Ru complex having a dearomatized pyridine-based pincer PN3P* ligand. This complex shows reusability for the high-pressure DFA in 1,4-dioxiane while maintaining the catalytic performance, however, deactivation occurred in other solvents. In dimethyl sulfoxide, its decomposition products may cause catalytic deactivation. The gas pressure generated in 1,4-dioxane was lower than that in water due to the high dissolution of 1,4-dioxane into CO2 according the vapor-liquid equilibrium calculations. The role of solvent is crucial since it affected the catalytic performance and also the generated gas pressure (H2 and CO2) from FA.

Computationally guided design of a new Rh catalyst for selective formic acid dehydrogenation: Validation with caution

Formic acid possesses many desirable properties as a promising hydrogen energy carrier. Density functional theory (DFT) was utilized to design new Rh complexes with 2,2′-biimidazoline ligands to explore their potential as catalysts for formic acid dehydrogenation. These designed complexes were prepared and examined as catalysts under various temperatures and ratios of formic acid to sodium formate. It was found that although our complexes gave a high TOF of 20,000 h−1 at 90 °C under certain formic acid/sodium formate ratios, the dehydrogenation reaction was prematurely deactivated once 30% of the formic acid was consumed. Possible deactivation mechanisms were investigated by NMR and HRMS. Our observations suggest that while guided rational design of catalysts by DFT has much potential, the method does have limitations as evidenced by our experimental comparisons and thus pure DFT design should be conducted with caution.

A Simple and Effective Principle for a Rational Design of Heterogeneous Catalysts for Dehydrogenation of Formic Acid.

Efficient and selective dehydrogenation of formic acid is a key challenge for a fuel-cell-based hydrogen economy. Though the development of heterogeneous catalysts has received much progress, their catalytic activity remains insufficient. Moreover, the design principle of such catalysts are still unclear. Here, experimental and theoretical studies on a series of mono-/bi-metallic nanoparticles supported on a NH2 -N-rGO substrate are combined for formic acid dehydrogenation where the surface energy of a metal is taken as a relevant indicator for the adsorption ability of the catalyst for guiding catalyst design. The AuPd/NH2 -N-rGO catalyst shows record catalytic activity by reducing the energy barrier of rate controlling steps of formate adsorption and hydrogen desorption. The obtained excellent results both in experiments and simulations could be extended to other important systems, providing a general guideline to design more efficient catalysts.

Assessment of van der Waals inclusive density functional theory methods for adsorption and selective dehydrogenation of formic acid on Pt(111) surface.

In this work, we studied the adsorption and catalytic dehydrogenation of formic acid (HCOOH) on Pt(111) surface using different van der Waals inclusive density functional theory (DFT) methods. Our results indicate that the PBE + dDsC method has the best overall performance on the description of adsorption and catalytic selectivity. We found the improved van der Waals (vdW) corrected methods (PBE + D3, PBE + TS, PBE + TS-SCS, PBE + TS/IH, PBE + MBD@rsSCS, and PBE + dDsC) and optimized vdW functionals (optPBE-vdW, optB88-vdW, and optB86b-vdW) perform well to estimate the adsorption energies of HCOOH and HCOO molecules on Pt(111) surface. The vdW-inclusive DFT approaches as well as the conventional PBE functional predict a higher activation barrier for C-H breaking by comparison of O-H breaking in the selective dehydrogenation of formic acid. However, the optimized vdW functionals evidently underestimate the rate constant of C-H breaking reaction, and then fail to describe the catalytic selectivity of the HCOOH's dehydrogenation. Both PBE + dDsC and PBE predict a similar temperature dependence of the ratio of reaction rate constants for O-H breaking versus C-H breaking, though PBE functional underestimate the adsorption energies.

Base-Free Dehydrogenation of Aqueous and Neat Formic Acid with Iridium(III) Cp*(dipyridylamine) Catalysts.

The selective dehydrogenation of formic acid by iridium(III) Cp*(dipyridylamine) catalysts is reported. The electron-enriched catalyst [IrIII Cp*{(4-dimethylaminopyridin-2-yl-κΝ)(pyridin-2'-yl-κΝ)amine}(OSO3 )] gave the best performances enabling the base free dehydrogenation of aqueous and neat formic acid. In both cases the reaction was selective with no carbon monoxide detectable. The IrIII complex demonstrated latent behavior, which may be of practical utility. Experimental results suggest an outer-sphere interaction with the ligand.

Highly Efficient Base-Free Dehydrogenation of Formic Acid at Low Temperature.

The ruthenium complex [RuH2 (PPh3 )4 ] is a competent catalyst for the selective dehydrogenation of formic acid (FA) at low temperature. It tolerates water and shows excellent performance (TOF up to 36 000 h-1 at 60 °C). Remarkably, no basic additives are necessary to obtain such high activity and the defined complex is stable for up to 120 days, making this system one of the most effective formic acid dehydrogenation catalysts known to date.

Homogeneous Catalytic Formic Acid Dehydrogenation in Aqueous Solution using Ruthenium Arene Phosphine Catalysts

In this work, we studied catalytic formic acid dehydrogenation with a homogeneous RAPTA type precatalyst in aqueous solution. The effects of an amino group, attached to the arene, and the impact of a second equivalent of 1,3,5‐triaza‐7‐phosphaadamantane (PTA) added in situ to the reaction were evaluated. The initial compound, [(η6‐benzyldimethylamine)Ru(PTA)Cl2]Cl (3), was synthesized and proved to be moderately active for selective formic acid dehydrogenation. The addition of a second equivalent of PTA at the beginning of the reaction significantly improved the catalytic performance. The activation energies for both catalytic systems were assessed via an Arrhenius plot. 1H ‐and 13C‐NMR spectroscopy was used to follow the course of the reaction online and verified complete consumption of substrate. A triplet signal was observed in the hydride region along with its corresponding coupling counterpart in 31P spectra.

Anchoring and Upgrading Ultrafine NiPd on Room-Temperature-Synthesized Bifunctional NH2 -N-rGO toward Low-Cost and Highly Efficient Catalysts for Selective Formic Acid Dehydrogenation.

Hydrogen is widely considered to be a sustainable and clean energy alternative to the use of fossil fuels in the future. Its high hydrogen content, nontoxicity, and liquid state at room temperature make formic acid a promising hydrogen carrier. Designing highly efficient and low-cost heterogeneous catalysts is a major challenge for realizing the practical application of formic acid in the fuel-cell-based hydrogen economy. Herein, a simple but effective and rapid strategy is proposed, which demonstrates the synthesis of NiPd bimetallic ultrafine particles (UPs) supported on NH2 -functionalized and N-doped reduced graphene oxide (NH2 -N-rGO) at room temperature. The introduction of the NH2 N group to rGO is the key reason for the formation of the ultrafine and well-dispersed Ni0.4 Pd0.6 UPs (1.8 nm) with relatively large surface area and more active sites. Surprisingly, the as-prepared low-cost NiPd/NH2 -N-rGO dsiplays excellent hydrophilicity, 100% H2 selectivity, 100% conversion, and remarkable catalytic activity (up to 954.3 mol H2 (mol catalyst)-1 h-1 ) for FA decomposition at room temperature even with no additive, which is much higher than that of the best catalysts so far reported.