Iron hydroxide, catalytic activity

Basic oxides of metals such as Co, Mn, Fe, and Cu catalyze the decomposition of chlorate by lowering the decomposition temperature. Consequendy, less fuel is needed and the reaction continues at a lower temperature. Cobalt metal, which forms the basic oxide in situ, lowers the decomposition of pure sodium chlorate from 478 to 280°C while serving as fuel (6,7). Composition of a cobalt-fueled system, compared with an iron-fueled system, is 90 wt % NaClO, 4 wt % Co, and 6 wt % glass fiber vs 86% NaClO, 4% Fe, 6% glass fiber, and 4% BaO. Initiation of the former is at 270°C, compared to 370°C for the iron-fueled candle. Cobalt hydroxide produces a more pronounced lowering of the decomposition temperature than the metal alone, although the water produced by decomposition of the hydroxide to form the oxide is thought to increase chlorine contaminate levels. Alkaline earths and transition-metal ferrates also have catalytic activity and improve chlorine retention (8). 

Metalloenzymes with non-heme di-iron centers in which the two irons are bridged by an oxide (or a hydroxide) and carboxylate ligands (glutamate or aspartate) constitute an important class of enzymes. Two of these enzymes, methane monooxygenase (MMO) and ribonucleotide reductase (RNR) have very similar di-iron active sites, located in the subunits MMOH and R2 respectively. Despite their structural similarity, these metal centers catalyze very different chemical reactions. We have studied the enzymatic mechanisms of these enzymes to understand what determines their catalytic activity [24, 25, 39-41]. 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

The most conventional catalytic material since the work of Bergius has been iron sulfide in various types. Pyrite, pyrrhotite, and various nonstoi-chiometric sulfides are known, and pyrrotite is postulated as the active form. Its precursors are red mud, residue of bauxite after the separation of alumina, iron ores of various sources, synthetic and natural pyrites, fine iron particles, iron dust from converters, iron sulfate, iron hydroxide, etc. (32, 33). 

Saturating the electrolyte with iron(lll) hydroxide (e.g., by addition of aqueous solutions of ferric nitrate) and simultaneously adding cobaltous salts leads to in situ formation of a mixed Fe(llI)/Co(ll)/Co(IIl) deposit, which exhibits catalytic activity comparable to that of Fe304 shown by the current voltage curve in Fig. 11. Such mixed oxidic catalyst coatings are composed of very small oxide crystals, which evidently are dissolved upon current interruption due to dissociative oxide dissolution. The transfer of dissolved metal ions to the cathode followed by cathodic deposition of the metal, however, can be completely prohibited, if the potential of the cathode due to optimal electrocatalysis of cathodic hydrogen evolution proceeds with an over-... 

The catalyst was prepared as follows. Iron hydroxides (2 g) were exposed to aqueous sulfuric acid or aqueous ammonium sulfate (30 ml) on a filter paper. After drying, the materials were powered and calcined in air. The catalytic activities of various iron oxides with or without the sulfate treatment for the reaction of 2-propanol are summarized in Table VI. The Fe203 catalysts treated with 0.25-0.5 M H2S04 showed unexpectedly high activities for the reaction, though the reaction did not occur at all over the catalysts prepared by calcining Fe(OH)3. The treatment with ammonium... 

It is suggested that the anodic dissolution will be inhibited if the adsorbed anion and the reaction intermediate are stable and hardly dissolve in aqueous solution. On the contrary, if the reaction intermediate is relatively unstable and readily dissolves into aqueous solution, the anion will function as an electrocatalyst accelerating the metal dissolution rate. It is now common knowledge that hydroxide ions, OH, catalyze the anodic dissolution of metallic iron and nickel in acid solution [81,82]. It is also known that chloride ions inhibit the anodic dissolution of iron in acidic solution [83]. No clear-cut understanding is however seen in literature on why hydroxide ions catalyze but chloride ions inhibit the anodic dissolution of iron, even though the two kinds of anions are in the same group of hard base. We assume that the hardness level in the Lewis base of adsorbed anions will be one of the most effective factors that determine the catalytic activity of the adsorbates. Further clarification on the catalytic characteristics will require a quantum chemical approach to the adsorption of these anions on the metal surface. 

This coordination makes the complexes water soluble over a large pH range. This effect is important in itself for if ionic iron were not precipitated as the hydroxides, at pH 10.46 it would have a catalytic activity comparable to that of catalase in the straightforward decomposition of hydrogen peroxide. 

The use of a mixed-valent, dinuclear iron site, similar to those in hemerythrin and ribonucleotide reductase,to catalyze a nonredox reaction such as phosphate ester hydrolysis is novel and unexpected for a variant of the familiar oxo(hydroxo)-bridged diiron center. In contrast to the general agreement that exists regarding the spectroscopic and physical properties of the PAPs, their kinetics properties and especially their mechanism of action remain controversial. Much of the disagreement stems from the different pH dependences of the catalytic activity of BSPAP and Uf, which is due to the fact that the former is isolated in a proteolytically activated form while the latter is not. Proteolysis results in a substantial increase in optimal pH in addition to an increase in catalytic activity at the optimal pH. "" Current data suggest that many of the spectroscopic studies described in the literature were performed on a catalytically inactive form of the enzyme. As a result, the roles of the trivalent and divalent metal ions in catalysis and in particular the identity of the nucleophilic hydroxide that directly attacks the phosphate ester remain unresolved. 

There is stiU a dispute as to whether the catalytic activity of iron-containing zeotype materials, for example, Fe-ZSM-5, should be attributed to isomorphously substituted framework iron or to extra-framework iron oxide or iron hydroxide species that are highly dispersed in the material. These extra-framework iron species are present for two reasons, either because they were not incorporated into the framework during the synthesis or because they were ejected from the framework during postsynthesis treatments (such as calcination or other heat treatments). The unresolved issue of the origin of catalytic activity continues to be the subject of research, whereby state-of-the-art characterization techniques are being applied. 

Basifiska and Domka in 1993 reported [21] Fe-Ru catalysts for the WGS reaction. They took a, p, y or 5 iron hydroxide and impregnated with Rh followed by calcination at 400 or 600 °C. The catalysts were prepared by ruthenium chloride. The catalytic activity results are presented in Table 2.1. 

Inclusion of these cations does impart new catalytic activities, but in many cases the active site results from a metal ion that has left the framework and entered the pore space upon heating, especially in the presence of water vapour. This is thought to be the case for zinc- and gallium-containing solids used in the dehydrocyclisation of butane and propane to aromatics in the Cyclar process (Chapter 9). Boron, iron, chromium and vanadium all appear to leave the framework under harsh conditions. The incorporation of titanium and more recently tin into framework sites within silicates have become very important substitutions, because both titanosilicates and stannosilicates have been shown to contain stable Lewis acid sites of importance in selective oxidation catalysis. The metal atom can coordinate additional water molecules in the as-prepared material, but these can be removed by heating. In the synthesis of titanosilicates, titanium is usually added to the gel as the alkoxide, and synthesis performed in the absence of sodium hydroxide to avoid precipitation of sodium titanate or nanoparticulate titanium oxides. 

Arata and Hino found that better catalysts could be obtained by calcining Fe(OH)3 at 573 — 873 K. The hydroxide was prepared by hydrolyzing FeCls or Fe(N03)3 9H20. The alkylation reactions were carried out at room temperature with 50 cm of toluene solution (0.5 mol 1 ) of benzyl chloride, t-butyl chloride or acetyl chloride and 0.1 g (for benzylation or t-butylation) or 0.5g (for acetylation) of catalyst. Benzylation and t-butylation was completed within 2 min and 10 min, respectively. For acetylation with acetyl chloride, the reaction was slow, the conversion being 28% after 6 h of reaction. The reaction with acetyl bromide is slighdy faster conversion of 30% was obtained after 4 h.The isomer distribution of alkyltoluenes was 42% ortho, 6% meta and 52% para for benzylation and 3% meta and 97% para for butylation with /-butyl chloride. It was presumed that iron chloride formed on the surface of amorphous iron oxide by its reaction with hydrogen chloride is a catalytically active species for alkylation. 

---