Heteropoly compounds absorption

Heterogenous reactions, Sh/Nu ratio, 27 64 Heteroligand complex, 32 260-262 Heteropolyacids defined, 41 117 heteroatoms, 41 118, 120, 121 Prins reaction, 41 156 supported, 41 149-150 Heteropolyanions, 41 113, 117, 119-121 Heteropoly blues, 41 191 Heteropoly compounds absorption, 41 179-180, 190-191 acid-catalyzed reactions heterogeneous, 41 161-178 liquid phase, 41 150-161 acidic properties in solid state, 41 141-150 in solution, 41 139—14] catalysis, 41 114, 116-117, 190-191 as catalyst, 41 113-116, 117, 223-232... 

In this section, these influences will be described. Besides the acidic properties, the absorption properties of solid heteropolyacids for polar molecules are often critical in determining the catalytic function in pseudoliquid phase behavior. This is a new concept in heterogeneous catalysis by inorganic materials and is described separately in Section VI. With this behavior, reactions catalyzed by solid heteropoly compounds can be classified into three types surface type, bulk type I, and bulk type II (Sections VII and IX). Softness of the heteropolyanion is important for high catalytic activity, although the concept has not yet been sufficiently clarified. 

The reaction of tert-butyl alcohol and methanol to form MTBE is also catalyzed by heteropoly compounds (221-223). A relationship was found between the amount of pyridine sorbed in or on heteropoly compounds and tert-butyl alcohol conversion (221). The dependence of the rate on methanol partial pressure resembles that for the absorption of methanol in the bulk, suggesting pseudoliquid phase behavior (223). 

Fig. 47. Olefin-to-paraffin ratio in the product hydrocarbons from dimethyl ether conversion as a function of absorptivity of the heteropoly compounds, expressed in term of the absorption of dimethyl ether in surface layer units (1) PW 2 (H3PW1204o), (2) NaH2PW 2, (3) Na2HPW 2, (4) CsH2PW 2, (5) Cs25H05PWl2, (6) Cs2l8JHo.isPW12, (7) (NH4)H2PW12, (8) (NH4)2HPWI2, (9) (NH4)25Ho.5PW12, (10) 1,4-diazine, (11) 1,3-diazine, (12) 1,4-bis(aminomethyl)benzene, (13) triazine. (From Ref. 197.)...

A low-sensitivity method for determining V(V) has been based on the greenish-yellow colour of the tungstenphosphovanadic heteropoly acid, which is formed by V(V) in the presence of H3PO4 in -0.5 M H2SO4 [90-93]. The molar absorptivity of the coloured compound is 1.4 lO at 400 nm. The compound can be extracted into n-hexanol or MIBK. 

M H20)sf (M = Al, Cr, Fe, Co), so the existence of a chromophore [M(0)6] in every heteropoly anion was claimed. The absorption spectrum was measured for 2 (NH4)20 C02O3 10 M0O3 12 H2O, too since the spectnxm exhibited an absorption band characteristic of a p-hydroxo polynuclear complex in addition to d-d absorption bands, the compound was considered to have a kind of polynuclear structure. 

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