Hydrogenation Of Bicarbonate Research Articles

Water-soluble (η 6-arene)ruthenium(II)-phosphine complexes and their catalytic activity in the hydrogenation of bicarbonate in aqueous solution

The reactions of [(η 6-C 6H 6)RuCl 2] 2 and [(η 6- p-cymene)RuCl 2] 2 with hydrogen in the presence of the water-soluble phosphines tppts ( meta-trisulfonated triphenylphosphine) and pta (1,3,5-triaza-7-phosphaadamantane) afforded as the main species [(η 6-C 6H 6)RuH(tppts) 2] +, [(η 6-C 6H 6)RuH(pta) 2] +, [(η 6- p-cymene)RuH(tppts) 2] + and [(η 6- p-cymene)RuH(pta) 2] +. This latter complex was also formed in the reaction of [(η 6- p-cymene)RuCl 2(pta)] and hydrogen with a redistribution of pta. In addition, prolonged hydrogenation at elevated temperatures and in the presence of excess of pta led to the formation of the arene-free [RuH(pta) 4Cl], [RuH(pta) 4(H 2O)] +, [RuH 2(pta) 4] and [RuH(pta) 5] + complexes. Ru-hydrides, such as [(η 6-arene)RuH(L) 2] +, catalyzed the hydrogenation of bicarbonate to formate in aqueous solutions at p(H 2)=100 bar, T=50–70 °C.

Chemometric modelling of the catalytic hydrogenation of bicarbonate to formate in aqueous media

The catalytic hydrogenation of aqueous bicarbonate was modelled utilizing a central composite experimental design. The results were compared with a dataset derived from a measurement procedure where univariate evaluations of the possible reaction conditions were applied. The results show good correlation between the measured and the modelled data. The optimum conditions to produce the highest possible formate concentration was identified by response surface methodology.

Homogeneous hydrogenation of carbon dioxide and bicarbonate in aqueous solution catalyzed by water-soluble ruthenium(II) phosphine complexes

The water-soluble Ru(II)–phosphine complex, [{RuCl 2( mTPPMS) 2} 2] was found a suitable catalyst for the hydrogenation of NaHCO 3 to NaHCO 2 in aqueous solution under mild conditions with catalyst turnover frequencies (TOFs) in the range of 35–50 h −1 at 50 °C and 10 bar total pressure. The suggested reaction mechanism involves the formation of Ru(II)-hydrides of the general formula [RuHX( mTPPMS) 4] where X=H −, HCO 3 − or HCO 2 −. At 80 °C and 95 bar total pressure, the reduction of NaHCO 3 proceeded with high reaction rate (9600 h −1) hitherto unobserved in purely aqueous solutions. The reactions do not require the presence of organic amine additives, however, the addition of quinoline increased the rate considerably. Aqueous suspensions of calcium carbonate could also be hydrogenated with CO 2/H 2 gas mixtures.

Water-soluble analogs of [RuCl3(NO)(PPh3)2] and their catalytic activity in the hydrogenation of carbon dioxide and bicarbonate in aqueous solution

The new water-soluble ruthenium-nitrosyl complexes [RuCl3(NO)(TPPMS)2] and [RuCl3(NO)(TPPTS)2] were synthetized and characterized by IR, 1H and 31P NMR spectroscopies. The NO stretching frequencies, νNO=1870 cm−1 (TPPMS) and 1883 cm−1 (TPPTS) suggest a linear Ru–N–O arrangements. Reactions with OH− yield the corresponding [RuCl3(NO2)(P)2] derivatives, furthermore, [RuH(NO)(P)3] is formed with TPPMS or TPPTS, respectively, under 100 bar H2 pressure. The new complexes are suitable precatalysts for the hydrogenation of carbon dioxide and/or bicarbonate in aqueous solutions up to a turnover frequency of 400 h−1 under relatively mild conditions (30 bar H2, 70 °C).

Formation and characterization of water-soluble hydrido-ruthenium(II) complexes of 1,3,5-triaza-7-phosphaadamantane and their catalytic activity in hydrogenation of CO2 and HCO3- in aqueous solution.

The water-soluble tertiary phosphine complex of ruthenium(II), [RuCl2(PTA)4], (PTA = 1,3,5-triaza-7-phosphaadamantane) was used as catalyst precursor for hydrogenation of CO2 and bicarbonate in aqueous solution, in the absence of amine or other additives, under mild conditions. Reaction of [RuCl2(PTA)4] and H2 (60 bar) gives the hydrides [RuH2(PTA)4] (at pH = 12.0) and [RuH(PTA)4X] (X = Cl- or H2O) (at pH = 2.0). In presence of excess PTA, formation of the unparalleled cationic pentakis-phosphino species, [HRu(PTA)5]+, was unambiguously established by 1H and 31P NMR measurements. The same hydrides were observed when [Ru(H2O)6][tos]2 (tos = toluene-4-sulfonate) reacted with PTA under H2 pressure. The rate of CO2 hydrogenation strongly depends on the pH. The highest initial reaction rate (TOF = 807.3 h(-1)) was determined for a 10% HCO3-/90% CO2 mixture (pH = 5.86), whereas the reduction was very slow both at low and high pH (CO2 and Na2CO3 solutions, respectively). 1H and 31P NMR studies together with the kinetic measurements suggested that HCO3- was the real substrate and [RuH(PTA)4X] the catalytically active hydride species in this reaction. Hydrogenation of HCO3- showed an induction period which could be ascribed to the slow formation of the catalytically active hydride species.

In-SituInfrared Study of Methanol Synthesis from H2/CO2over Cu/SiO2and Cu/ZrO2/SiO2

The interactions of CO2and H2/CO2with Cu/SiO2, ZrO2/SiO2, and Cu/ZrO2/SiO2have been investigated byin-situinfrared spectroscopy with the aim of understanding the nature of the species involved in methanol synthesis and the dynamics of the formation and consumption of these species. In the case of Cu/SiO2, the only species observed during methanol synthesis are formate groups on Cu and methoxide groups on silica. When ZrO2/SiO2or Cu/ZrO2/SiO2is exposed to H2/CO2the majority of the species observed are associated with ZrO2. CO2adsorption on either ZrO2/SiO2or Cu/ZrO2/SiO2leads to the appearance of carbonate and bicarbonate species on the surface of ZrO2. In the presence of H2these species are converted to formate and then methoxide species adsorbed on ZrO2. The presence of Cu greatly accelerates the hydrogenation of bicarbonate to formate species, and the hydrogenation of formate to methoxide species. On Cu/ZrO2/SiO2methylenebisoxy species are observed as intermediates in the latter reaction. While Cu promotes the reductive elimination of methoxide species as methanol, it is observed that hydrolytic release of methoxide species from ZrO2occurs much more rapidly than reductive elimination. Thus, the methanol synthesis over Cu/ZrO2/SiO2is envisioned to occur on ZrO2, with the primary role of Cu being the dissociative adsorption of H2. The spillover of atomic H onto ZrO2provides the source of hydrogen needed to hydrogenate the carbon-containing species. It is also proposed that the formation of CO via the reverse-water–gas-shift reaction occurs on Cu.

The heterogeneous catalytic hydrogenation of bicarbonate to formate in aqueous solutions

The kinetics of the hydrogenation of aqueous solutions of HCO 3 − to HCO 2 − over Pd on C catalysts was studied. It was shown that the rate rose with increasing H 2 pressure in accordance with a Langmuir isotherm law. With increasing HCO 3 − concentration the rate passed through a maximum. Measurements of the equilibrium at 35 °C indicated a Gibbs free energy change of about −2.2 kcal/ mole. The highest concentration of HCO 2 − obtainable at 6 atm H 2 was limited by the common ion effect to 5.8 M.

The Hydrogenation of Sodium Bicarbonate to Sodium Formate

The Hydrogenation of Sodium Bicarbonate to Sodium Formate