Catalytic oxidation of formic acid

Zhao, H., et al., Fabrication of a palladium nanoparticle/graphene nanosheet hybrid via sacrifice of a copper template and its application in catalytic oxidation of formic acid. 

The formate, formed by oxidative dehydrogenation of the acid, is quite stable and doesn t decompose until 480 K. This decomposition is a classical first-order case with a decomposition activation energy of 130 kJ mol-1 and a normal value pre-exponential of 1013 s-1. The great ability of the TPD technique is the separation of the individual steps in the reaction in temperature. It is clear that the step proceeding over the highest barrier in this case is the formate decomposition, and that in a catalytic oxidation of formic acid the most abundant surface intermediate is likely to be the formate with its decomposition being rate determining. 

Vospemik et al. (2006) calculated the profile concentration along the porous catalytic layer by assuming the gas-liquid interface at the border between an intermediate porous catalytic layer and the coarse support (at about 50 pm from the top-layer surface). In their model they considered the complete depletion of oxygen in the reaction zone during the catalytic oxidation of formic acid. Their model did not take into account the catalyst distribution along the cross-section. They found the limiting influence of oxygen diffusion on the overall reaction rate. 

Baldi, G., S. Goto, C. K. Chow and J. M. Smith. Catalytic Oxidation of Formic Acid in Water. Ind. Chem. Eng. Proc. 

Baldi G, Goto S, Chow C-K, Smith JM (1974) Catalytic oxidation of formic acid in water. Intraparticle diffusion in liquid-filled pores Ind Eng Chem Process Design Dev 13 447-452... 

There is an extensive literature relating to the role of surface intermediates in the heterogeneous catalytic decomposition of formic acid on metals and oxides (see Refs. 36, 522,1030,1042—1045). 

For the purpose of demonstrating the effects of surface coverage by Pd, 0pd, on the rate of electro-oxidation of formic acid and the ORR, Fig. 8.17 reveals that the i versus 0Pd relationship again has a volcano-like form, with the maximum catalytic activity being exhibited for 1 ML of Pd. The examples that we have given indicate that volcano relationships are the rule rather than the exception, emphasizing the importance of a systematic evaluation of the catalyst factors that control catalytic activity. A thorough... 

The effects of a-CD on the bromination of other substrates have been studied recently (Javed, 1990 Tee et al., 1990a Tee and Javed, 1993), the object being to see if the catalytic effects observed earlier with phenols (Tee and Bennett, 1988a) are peculiar to these substrates or more general. Broadly speaking, various aromatic and heteroaromatic substrates (Table A4.4) showed behaviour (k /k2u = 1.7 to 10 XTS = 0.2 to 1.2 mM) very similar to that of phenols, and so the catalytic effect appears to be fairly general. The oxidation of formic acid by bromine also shows catalysis by a-CD (Han et al., 1989 Tee et al., 1990a). 

Ion implantation has also been used for the creation of novel catalytically active materials. Ruthenium oxide is used as an electrode for chlorine production because of its superior corrosion resistance. Platinum was implanted in ruthenium oxide and the performance of the catalyst tested with respect to the oxidation of formic acid and methanol (fuel cell reactions) (131). The implantation of platinum produced of which a catalytically active electrode, the performance of which is superior to both pure and smooth platinum. It also has good long-term stability. The most interesting finding, however, is the complete inactivity of the electrode for the methanol oxidation. 

An intermediate involving oxidant, substrate, and catalyst is formed in the Cr(IH)-catalysed oxidation of formic acid by Ce(IV) in aqueous sulfuric acid medium. A Cr(III)/Cr(IV) catalytic cycle operates in the reaction.192... 

The oxidation of formic acid was one of the first electrocatalytic oxidations at ECP modified by platinum particles, which was studied by Gholamian et al. [27]. They observed that the incorporation of O.lmgcm of Pt into a PAni film enhanced greatly the oxidation rate of formic acid (10 times enhancement). They evaluated the optimum film thickness (around 1 pm) for a maximum enhancement of the oxidation current. They also determined the resistance profile of the PAni film correlatively to the catalytic activity of the Pt particles and found that the maximum electroactivity occurs within the conducting potential window of the polymer. However, this correlation is not definitively established since they do not determine the conductivity of the PAni film in the presence of Pt particles, which must be higher than in the absence of the metallic particles. 

Results of Investigations on the Catalytic Decomposition of Formic Acid on Oxides (—H, dehydrogenation -CO dehydration)... 

The affinity for oxygen of the metal involved determines whether reactions of type I or type II occur. Nickel formate produces nickel, magnesium formate produces magnesium oxide. Of special interest to us, however, is the extent to which reactions of type a or b occur, and whether the Ia/Ib or the Ila/IIb ratio is in any way related to the selectivity of the catalytic decomposition of formic acid on the metals and oxides in question. Furthermore it is worth while to investigate whether the stability of the bulk formates (e.g., the decomposition temperature) bears a relation to the catalytic activity of the corresponding metals or oxides. 

Considering these precedents, it is no wonder that during the last 2 years most of the papers devoted to the study of oxidation of formic acid are dealing with the problem of how the catalytic activity can be enhanced or the poison formation can be minimized by adatoms or other species (acetonitrile, nitromethane). °... 

The combination of two catalytic elements was realized in a study of formic acid oxidation on Pt(lOO) and Pt(lll) modified by the adsorption of palladium [Pdaj + Pt(lOO) and Pdjd + Pt(lll) systems]. While the presence of adsorbed palladium on Pt(lOO) resulted in a considerable lowering of the oxidation potential and the absence of self-poisoning under open circuit conditions, the activity of Pt(lll) substrate did not change significantly by Pd adsorption. However, a deactivation of the Pdaj + Pt(lOO) system is observed when the oxidation of formic acid takes place. This deactivation is analyzed in terms of slow formation of an adsorbed species blocking the initial step of formic acid oxidation on palladium sites. 

The kinetics of the catalytic decomposition of formic acid on sodium tungsten bronzes Naj,W03, with x in the range 0.11—0.85, and on tungstic oxide have been investigated manometrically in a static system at 150— 250 °C with acid pressures of 25—30 Torr. The decomposition products were CO2, CO, H2O, and Hg, the mole ratios C02 CO and H2 C02 being determined mass-spectrometrically. 

In this way, a catalytic eff t of Pb on die electro-oxidation of formic acid was clearly observed when its respcmse was compared with the response obtained with the respective Pt/Polymer-Pt electrode under the same conditions. A noticeable increase in the curratit peaks associated with die direct oxidation of the substrate is observed in the tfam cases along with a clear decrease in the charge assigned to the oxidation of strongty adsorbed intermediates near 0.74 V. This observation confirms that the presence of lead precludes the fixation of poisoning intermediate species on platinum. It is necessaiy to emphasize that the presence of Pb(U) in die electrolyte is not required to obtain the j-t response for these modified electrodes. 

In the first case, the activity of the surface is directly proportional to the number of pair ad-atom-surface sites, whereas in the latter case, the activity is proportional to the number of unoccupied surface sites. Since oxidation of formic acid takes place though a parallel-path mechanism, the effects of different levels of poisoning are also considered. For the cases in which the surface is completely covered by poison, both types of ad-atoms (the catalytically effective ad-atoms and the third-body adatoms) produce similar qualitative effects, that is, both types increases the current for the oxidation of formic acid [65]. Of course, the catalytic enhancement is higher in the case of the ad-atoms that modifies the electronic properties of the surface, since the global effect will be the combination of the electronic enhancement and the third-body effect (any ad-atom always acts as a third body). This is the case, for instance, for the Pt(lOO) surfaces modified with ad-atoms [65-67]. For the surfaces with low poisoning, that is, the Pt(lll)... 

The method of catalyst preparation (especially in the case of alloys) and the catalyst interaction with the polymer support matrix play important roles in determining the resultant electrocatalytic effect. The catalyst/support couple PtSn/PAni (0.5 pm thickness) with PtSn synthesized by electroreduction at 0.1 V vs. RHE was found to be an effective catalytic system for formic acid oxidation, lowering the anode potential by over 100 mV compared to pure Pt/PAni and PtRu/PAni [324]. Moreover, the oxidation of formic acid on PtSn/PAni commences at low potentials, in the hydrogen adsorption region, around 0.1-0.2 V vs. RHE. 

The acidity and basicity increase when ZnO is mixed with other oxides. ZnO —Ti02 becomes more acidic and reveals high activity for hydration of ethylene. Both acid and base amounts increase upon mixing with Si02 and isomerization of butene is catalyzed by the acid sites of ZnO — SiOz Addition of K to ZnO increased the base amount, and the catalytic activity for oxidation of formic acid sharply increased.A mixed oxide catalyst consisting of ZnO and FezOa is a good basic catalyst for the methylation by methanol of phenol to 2,6-xylenol. ... 

Trillo JM, Munuera G, Criado JM (1972) Catalytic decomposition of formic acid on metal oxides. Catal Rev 7 51-86... 

Brandt, K., Steinhausen, M., and Wandelt, K. (2008) Catalytic and electroformic acid on the pure and Cu-modified Pd(lll)-surface./. Bectroanal. Chem., 616, 27-37. 

Other potential processes for production of formic acid that have been patented but not yet commerciali2ed include Hquid-phase oxidation (31) of methanol to methyl formate, and hydrogenation of carbon dioxide (32). The catalytic dehydrogenation of methanol to methyl formate (33) has not yet been adapted for formic acid production. 

Liquid-Phase Oxidation. Liquid-phase catalytic oxidation of / -butane is a minor production route for acetic acid manufacture. Formic acid (qv) also is produced commercially by Hquid-phase oxidation of / -butane (18) (see HYDROCARBON OXIDATION). 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

Catalytic oxidation of isobutyraldehyde with air at 30—50°C gives isobutyric acid [79-31-2] ia 95% yield (5). Certain enzymes, such as horseradish peroxidase, cataly2e the reaction of isobutyraldehyde with molecular oxygen to form triplet-state acetone and formic acid with simultaneous chemiluminescence (6). 

Polypyrrole shows catalytic activity for the oxidation of ascorbic acid,221,222 catechols,221 and the quinone-hydroquinone couple 223 Polyaniline is active for the quinone-hydroquinone and Fe3+/Fe2+ couples,224,225 oxidation of hydrazine226 and formic acid,227 and reduction of nitric acid228 Poly(p-phenylene) is active for the oxidation of reduced nicotinamide adenine dinucleotide (NADH), catechol, ascorbic acid, acetaminophen, and p-aminophenol.229 Poly(3-methylthiophene) catalyzes the electrochemistry of a large number of neurotransmitters.230... 

The qualitative voltammetric behavior of methanol oxidation on Pt is very similar to that of formic acid. The voltammetry for the oxidation of methanol on Pt single crystals shows a clear hysteresis between the positive- and negative-going scans due to the accumulation of the poisoning intermediate at low potentials and its oxidation above 0.7 V (vs. RHE) [Lamy et al., 1982]. Additionally, the reaction is also very sensitive to the surface stmcture. The order in the activity of the different low index planes of Pt follows the same order than that observed for formic acid. Thus, the Pt(l 11) electrode has the lowest catalytic activity and the smallest hysteresis, indicating that both paths of the reaction are slow, whereas the Pt( 100) electrode displays a much higher catalytic activity and a fast poisoning reaction. As before, the activity of the Pt(l 10) electrode depends on the pretreatment of the surface (Fig. 6.17). 

Another important difference in the poison formation reaction is observed when studying this reaction on Pt(lll) electrodes covered with different adatoms. On Pt(lll) electrodes covered with bismuth, the formation of CO ceased at relatively high coverages only when isolated Pt sites were found on the surface [Herrero et al., 1993]. For formic acid, the formation takes place only at defects thus, small bismuth coverages are able to stop poison formation [Herrero et al., 1993 Macia et al., 1999]. Thus, an ideal Pt(lll) electrode would form CO from methanol but not from formic acid. This important difference indicates that the mechanism proposed in (6.17) is not vahd. It should be noted that the most difhcult step in the oxidation mechanism of methanol is probably the addition of the oxygen atom required to yield CO2. In the case of formic acid, this step is not necessary, since the molecule has already two oxygen atoms. For that reason, the adatoms that enhance formic acid oxidation, such as bismuth or palladium, do not show any catalytic effect for methanol oxidation. 

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