Oxides, metal, reactions formaldehyde

Control of reaction paths on catalyst surfaces by optimizing the structure and electronic properties is a key issue to be solved in surface science. Iron/molybdenum oxides are used as industrial catalysts for methanol oxidation to form formaldehyde selectively. The iron /molybdenum oxide catalyst consists of Fe2(Mo04)3 and M0O3, and shows kinetics and selectivity similar to those of M0O3 for methanol oxidation [Ij. It suggests that Mo-O sites play an important role in the reaction. M0O3 has a layered structure along a (010) plane, but the (010) surface is not reactive because it has no unsaturated Mo site [1]. On Mo metal surfaces such as (100) [2,3] and (112) [4], major products in methanol reactions were H2 and CO. Therefore, we considered that partial oxidation of Mo sites is needed for the selective oxidation of methanol. We have reported that methanol reaction pathways on Mo(l 12) could... 

A great number of catalysts have been tried in the oxidation of methane at atmospheric pressure with the hope of obtaining intermediate products of oxidation. It appears, however, that catalysts tend to carry the reaction to equilibrium, at which state methanol, formaldehyde and formic acid are present in only extremely minute traces. This is well illustrated by the work of Wheeler and Blair," who studied the influence of catalysts in connection with their work on the mechanism of combustion. When methane was oxidized in the presence of metallic and metallic oxide catalysts, no formaldehyde could be detected even at very short times of contact. The formaldehyde produced in the circulation experiments was in a concentration much greater than that required for equilibrium in the reaction ... 

On the other hand, the oxidative coupling reaction of CH4 in the presence of Og, even when performed in membrane-type reactors, is mainly catalysed by metal oxide catalysts. Also oligomerisation, aromatisation and the partial oxidation to methanol or formaldehyde apply non-metallic heterogeneous catalysts (i.e. zeolites, supported metal oxides or heterogenized metalcarbon nanofibers or nanotubes from methane, these being catalysed by metal nanoparticles, but at the moment this is not considered as a Cl chemistry reaction. Again we direct the attention of the reader to some reviews on this type of process. ... 

In the 1920 s, E. MQller and his co-workers made a series of studies on the anodic oxidation of methanol, formaldehyde, and formic acid which represent the first extensive mechanistic investigation of these compounds, although the principles of electrode kinetics had not yet been formulated. Muller did not establish mechanisms for these reactions however, many of his observations have been later confirmed and his studies were among the first with a comparison of polarization curves on several noble metals including platinum, palladium, rhodium, iridium, osmium, rubidium, gold, and silver (cf. Figure 1). As was usual at that time, Muller discussed his results in terms of polarization, rather than in terms of current or reaction rate. 

The reaction is generally carried out at atmospheric pressure and at 350—400°C. A variety of catalysts, eg, bases and metal salts and oxides on siUca or alumina—sihcates, have been patented (86—91). Conversions are in the 30—70% range and selectivities in the 60—90% range, depending on the catalyst and the ratio of formaldehyde to acetate. 

Formaldehyde is readily reduced to methanol by hydrogen over many metal and metal oxide catalysts. It is oxidized to formic acid or carbon dioxide and water. The Cannizzaro reaction gives formic acid and methanol. Similarly, a vapor-phase Tischenko reaction is catalyzed by copper (34) and boric acid (38) to produce methyl formate ... 

Most of the world s commercial formaldehyde is manufactured from methanol and air either by a process using a silver catalyst or one using a metal oxide catalyst. Reactor feed to the former is on the methanol-rich side of a flammable mixture and virtually complete reaction of oxygen is obtained conversely, feed to the metal oxide catalyst is lean in methanol and almost complete conversion of methanol is achieved. 

Acid catalysts, such as metal oxides and sulfonic acids, generally catalyze condensation polymerizations. However, some condensation polymers form under alkaline conditions. For example, the reaction of formaldehyde with phenol under alkaline conditions produces methy-lolphenols, which further condense to a thermosetting polymer. 

Redox reactions with metal porphyrins (MPs) as photocatalysts. A spectacular example here is the reaction that couples upon illumination with the sunlight, methanol oxidation to formaldehyde with the formation of hydrogen peroxide in be nzene-methanol mixture (90 10)... 

Together with the fast oxidation (at low temperatures) of NO to N02, the plasma causes the partial HC oxidation (using propylene, the formation of CO, C02, acetaldehyde and formaldehyde was observed). Both the effects cause a large promotion in activity of the downstream catalyst [86]. For example, a "/-alumina catalyst which is essentially inactive in the SCR of NO with propene at temperatures 200°C allows the conversion of NO of about 80% (in the presence of NTP). Formation of aldehydes follows the trend of NO concentration suggesting their role in the reaction mechanism. Metal oxides such as alumina, zirconia or metal-containing zeolites (Ba/Y, for example) have been used [84-87], but a systematic screening of the catalysts to be used together with NTP was not carried out. Therefore, considerable improvements may still be expected. 

Formaldehyde manufacture, 12 113-117. See also Formaldehyde production by exothermic reaction, 12 115 metal oxide catalyst, 12 115-117 methanol process for, 12 113 new processes for, 12 117 silver catalyst, 12 113-115 Formaldehyde plant... 

Beyer and coworkers later extended these reactions to platinum clusters Ptn and have demonstrated that similar reaction sequences for the oxidation of carbon monoxide can occur with larger clusters [70]. In addition, they were able to demonstrate poisoning effects as a function of surface coverage and cluster size. A related sequence for Pt anions was proposed by Shi and Ervin who employed molecular oxygen rather than N2O as the oxidant [71]. Further, the group of Bohme has screened the mononuclear cations of almost the entire transition metal block for this particular kind of oxidation catalysis [72,73]. Another catalytic system has been proposed by Waters et al. in which a dimolybdate anion cluster brings about the oxidation of methanol to formaldehyde with nitromethane, however, a rather unusual terminal oxidant was employed [74]. 

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