Metal sulfates selectivity

Strong acids are able to donate protons to a reactant and to take them back. Into this class fall the common acids, aluminum hahdes, and boron trifluoride. Also acid in nature are silica, alumina, alumi-nosihcates, metal sulfates and phosphates, and sulfonated ion exchange resins. They can transfer protons to hydrocarbons acting as weak bases. Zeolites are dehydrated aluminosilicates with small pores of narrow size distribution, to which is due their highly selective action since only molecules small enough to enter the pores can reacl . 

DeKock, C. W. Thermodynamic Properties of Selected Metal Sulfates and Their Hydrates, 1986, Bureau of Mines, Information Circular 9081. 

Lewis Acid-Complexed Metal Salts. Mixtures of aluminum chloride and metal chloride are known to be active for the isomerization of paraffins at room temperature.178 Ono and co-workers179-183 have shown that the mixtures of aluminum halides with metal sulfates are much more selective for similar reactions at room temperature. 

Some care must be exercised in selecting the chemical treatment. Thus, for example, metal sulfides can be converted to noninhibitory (but usually inactive) metal sulfates by reaction with O2. However, sulfates remain in the reactor and, in some cases, can be reconverted to sulfides on re-admission of H2. 

The acid strength of oxoacid salts in the solid state increases with the electronegativity of the metal ion, and hence catalytic activity increases with electronegativity. Figure 14 shows an example of selectivity, in which the selectivity of double bond isomerization of butene over metal sulfates changes with the electronegativity. ... 

Figure 14 Effect of acid strength on the selectivity observed for isomerization of cw-2-butene over metal sulfates...

P5C-6 The selective oxidation of toluene and methanol over vanadium pentoxide-sup-ported alkali metal sulfate catalysts was studied recently fAIOiEJ., 27(1), 41 (1981)]. Examine the experimental technique used (equipment, variables, etc.) in light of the mechanism proposed. Comment on the shortcomings of the analysis and compare with another study of this system presented in AZOiE J., 25(5), 855 (1982). 

Selected kinetic characteristics for the decompositions of metal sulfates... 

On the other hand, many metal sulfates generate fairly large amounts of acid sites of moderate or strong strength on their surfaces when they are calcined at 400-700)°C [1]. The acidic property of metal sulfate often gives high selectivity for diversified reactions such as hydration, polymerization, alkylation, cracking, and isomerization [1]. However, structural and physicochemical properties of supported metal sulfates are considered to be in different states compared with bulk metal sulfates because of their interaction with... 

In the present article, the discussion concentrates on the catalytic activity and selectivity of solid metal sulfates in terms of the acidic property (acidity, acid strength, and Bronsted and Lewis acids) by integrating the kinetic and structural studies. 

The selectivity of the metal sulfate catalyst is influenced by many factors besides its acidic property, such as geometric structure involving a pore structure, arrangement of basic sites, polarity of the surface, etc. For example, the relative values of the first-order rate constants (per imit acidity at pK — 3) of the depolymerization catalyzed by nickel sulfate, cupric sulfate, and silica-alumina were found to be 1100 300 1. The difference may be attributed to the differences in acid-base bi-functional catalysis of these catalysts. This view may be said to have originated in 1948 when Turkevich and Smith (45) showed that the isomerization of 1-butene to 2-butene is catalyzed by metal sulfates, sulfuric acid, phosphoric acid, etc., but little by acetic acid, hydrogen chloride, etc. The high catalytic activity of the catalysts of the former group is considered as due to acid-base bifunctional catalysis as illustrated by Fig. 14. Independently, Horiuti (45a) advanced the same idea... 

The selectivity aspect of metal sulfate catalysts needs further investigation to help clarify the structural nature of the sulfate catalysts. 

We have attempted to present an integrated picture on the acid property of solid metal sulfates as used in various heterogeneously catalyzed reactions, with some view presented on the surface structure. We saw some unusual catalytic activity and selectivity exhibited by these solid sulfates in diversified reactions which may surpass in some aspects those of a more universal catalyst represented by silica-alumina and its related oxides. 

The salen-based receptor 47 is an example of a selective extractant for metal sulfates. The ligand forms a complex involving deprotonated phenoUc hydroxyl groups and pro-tonated morpholine residues adapted for hydrogen bonding to the anion. The ligand readily extracts CUSO4 into chloroform solution, for example, with essentially 100% efficiency. ... 

Phenols can also be alkylated with olefins. The alkylation of m-cresol with propylene to produce thymol (2-isopropyl —5-methylphenol) was studied with metal sulfates and alumina as catalysts.A 90% selectivity to thymol was obtained at the phenol conversion of 63% from a 1 1 mixture of phenol and propylene at 673 K. 

The hydration of oleflns is important for the direct synthesis of alcohols from olefins in the pietroleum industry and has been extensively studied over various solid acid catalysts. In the case of ethanol synthesis from ethylene and water, silicotungstic acids, silicophosphoric acids, solid phosphoric acids, metal sulfates, " and metal oxides have been studied as solid acid catalysts. In its industrial process, a solid phosphoric acid catalyst (Shell patent) is widely used throughout the world. The nature of the active (acidic) sites which exhibit high catalytic activity and selectivity is discussed below together with the hydration mechanism involving the catalytic behavior. 

The electronegativity of metal ion, i, was first proposed by Tanaka, Oaaki, and Tamaru (Shokubai, 6, 262 (1964)) the values were calculated by the equation z - (1 +Z) xo — (1), where Z and xo are the oxidation number of metal ion and the electronegativity of metal as element, respectively. Later, Tanaka and Ozaki revised the values by using xi - (1 + 2Z) xo — (2). Since xi from eq. (1) did not fit the data, Misono el al derived an independent equation of xi - xo + (E/n)ii — (3), where / is the n-th ionization potential, in order to explain the catalytic activity and selectivity of metal sulfates for butene isomerization. However, there is fairly good correlation between the revised x-, from eq. (2) and Xi from eq. (3). The electronegativity used here is from eq. (3). ... 

In the preparation of highly active and selective Fe-Cu/Si02 catalyst for the partial hydrogenation of phenylacetylene, coprecipitation of 70% Fe and 30% Cu, the use of metal sulfates, and a relatively low precipitation temperature (around 20°C) were found to be very effective. The activity of this improved catalyst was three orders higher than the ordinal Fe/Si02 catalyst and the... 

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