A continuous-flow method for the generation of hydrogen from formic acid

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.

Formic Acid as a Potential On-Board Hydrogen Storage Method: Development of Homogeneous Noble Metal Catalysts for Dehydrogenation Reactions

Hydrogen can be used as an energy carrier for renewable energy to overcome the deficiency of its intrinsically intermittent supply. One of the most promising application of hydrogen energy is on-board hydrogen fuel cells. However, the lack of a safe, efficient, convenient, and low-cost storage and transportation method for hydrogen limits their application. The feasibility of mainstream hydrogen storage techniques for application in vehicles is briefly discussed in this Review. Formic acid (FA), which can reversibly be converted into hydrogen and carbon dioxide through catalysis, has significant potential for practical application. Historic developments and recent examples of homogeneous noble metal catalysts for FA dehydrogenation are covered, and the catalysts are classified based on their ligand types. The Review primarily focuses on the structure-function relationship between the ligands and their reactivity and aims to provide suggestions for designing new and efficient catalysts for H₂ generation from FA.

Decomposition of Additive-Free Formic Acid Using a Pd/C Catalyst in Flow: Experimental and CFD Modelling Studies

The use of hydrogen as a renewable fuel has gained increasing attention in recent years due to its abundance and efficiency. The decomposition of formic acid for hydrogen production under mild conditions of 30 °C has been investigated using a 5 wt.% Pd/C catalyst and a fixed bed microreactor. Furthermore, a comprehensive heterogeneous computational fluid dynamic (CFD) model has been developed to validate the experimental data. The results showed a very good agreement between the CFD studies and experimental work. Catalyst reusability studies have shown that after 10 reactivation processes, the activity of the catalyst can be restored to offer the same level of activity as the fresh sample of the catalyst. The CFD model was able to simulate the catalyst deactivation based on the production of the poisoning species CO, and a sound validation was obtained with the experimental data. Further studies demonstrated that the conversion of formic acid enhances with increasing temperature and decreasing liquid flow rate. Moreover, the CFD model established that the reaction system was devoid of any internal and external mass transfer limitations. The model developed can be used to successfully predict the decomposition of formic acid in microreactors for potential fuel cell applications.

Structural analysis of transient reaction intermediate in formic acid dehydrogenation catalysis using two-dimensional IR spectroscopy

The molecular structure of a catalytically active key intermediate is determined in solution by employing 2D IR spectroscopy measuring vibrational cross-angles. The formate intermediate (2) in the formic acid dehydrogenation reaction catalyzed by a phosphorus-nitrogen PN3P-Ru catalyst is elucidated. Our spectroscopic studies show that the complex features a formate ion directly attached to the Ru center as a ligand, and a proton added to the imine arm of the dearomatized PN3P* ligand. During the catalytic process, the imine arms are not only reversibly protonated and deprotonated, but also interacting with the protic substrate molecules, effectively serving as the local proton buffer to offer remarkable stability with a turnover number (TON) over one million.

Hydrogen generation from glucose catalyzed by organoruthenium catalysts under mild conditions

Concerns about the depletion of fossil fuel reserves and environmental pollution make hydrogen an attractive alternative energy source. Here, we first describe a catalytic reaction system that produces H₂ from glucose using a homogeneous catalyst [(p-cymene)Ru(NH₃)]Cl₂ with the maximum TOF = 719 h^-1 at 98 °C and an initial pH = 0.5.

Highly efficient dehydrogenation of formic acid in aqueous solution catalysed by an easily available water-soluble iridium(iii) dihydride

Water-soluble cis-mer-[IrH₂Cl(mtppms)₃] selectively dehydrogenated formic acid with a TOF of 298 000 h⁻¹, a final pressure of 140 bar, and a TON_max of 674 000.

Hydrogen energy future with formic acid: a renewable chemical hydrogen storage system

Formic acid, the simplest carboxylic acid, could serve as one of the better fuels for portable devices, vehicles and other energy-related applications in the future.

Iridicycle-Catalysed Imine Reduction: An Experimental and Computational Study of the Mechanism

The mechanism of imine reduction by formic acid with a single-site iridicycle catalyst has been investigated by density functional theory (DFT), NMR spectroscopy, and kinetic measurements. The NMR and kinetic studies suggest that the transfer hydrogenation is turnover-limited by the hydride formation step. The calculations reveal that, amongst a number of possibilities, hydride formation from the iridicycle and formate probably proceeds by an ion-pair mechanism, whereas the hydride transfer to the imino bond occurs in an outer-sphere manner. In the gas phase, in the most favourable pathway, the activation energies in the hydride formation and transfer steps are 26-28 and 7-8 kcal mol(-1) , respectively. Introducing one explicit methanol molecule into the modelling alters the energy barrier significantly, reducing the energies to around 18 and 2 kcal mol(-1) for the two steps, respectively. The DFT investigation further shows that methanol participates in the transition state of the turnover-limiting hydride formation step by hydrogen-bonding to the formate anion and thereby stabilising the ion pair.

High-quality hydrogen generated from formic acid triggered by in situ prepared Pd/C catalyst for fuel cells

High-quality hydrogen can be generated from formic acid triggered by in situ prepared Pd/C catalyst in ambient conditions. The obtained gas can be directly fed into proton exchange membrane fuel cells indicating a very promising application.

Interconversion between formic acid and H(2)/CO(2) using rhodium and ruthenium catalysts for CO(2) fixation and H(2) storage

The interconversion between formic acid and H(2)/CO(2) using half-sandwich rhodium and ruthenium catalysts with 4,4'-dihydroxy-2,2'-bipyridine (DHBP) was investigated. The influence of substituents of the bipyridine ligand was studied. Chemical shifts of protons in bipyridine linearly correlated with Hammett substituent constants. In the hydrogenation of CO(2) /bicarbonate to formate under basic conditions, significant activations of the catalysts were caused by the electronic effect of oxyanions generated by deprotonation of the hydroxyl group. Initial turnover frequencies of the ruthenium- and rhodium-DHBP complexes increased 65- and 8-fold, respectively, compared to the corresponding unsubstituted bipyridine complexes. In the decomposition of formic acid under acidic conditions, activity enhancement by the electronic effect of the hydroxyl group was observed for the ruthenium catalyst. The rhodium-DHBP catalyst showed high activity without CO contamination in a relatively wide pH range. Pressurized H(2) can be obtained using an autoclave reactor. The highest turnover frequency and number were obtained at 80 °C. The catalytic system provides valuable insight into the use of CO(2) as a H(2) storage material by combining CO(2) hydrogenation with formic acid decomposition.