CONTROLLED MODULATION OF MESOPOROSITIES IN METAL (M=AL, FE) PHOSPHATESOLIDS

Mesoporous solids which posses average pore diameters between 7 and 20 nm, depending on the composition, have been prepared. The solids have the general formula Al100P(x)M20 where M = Al or Fe, and x = 0, 4.5, 9, 18, 36, 72 or 144. The initial addition of phosphorus as phosphate transforms the originally crystalline oxide/oxides into amorphous soli ds. These amorphous materials posses a narrow pore size distribution: 80-90% of the pores lie within 1-2 nm of the average pore diameter. Su bsequent incremental amounts of phosphorus transform the material into a crystalline solid whilst the pore size distribution becomes much wi der and the maximum moves towards larger pore diameters. Substitution of 20% of the aluminium by iron results, at a low phosphorus content, in pores with smaller pore volumes and smaller surface areas. The data in the dV(p)/dD(p) = f(D(p)) graphs, where V(p) is the incremental po re volume and D(p) is the average pore diameter, can be approximated u sing an admixture of Gaussian and Lorentzian curves. For low phosphoru s contents the dV(p)/dD(p) = f(D(p)) curves have a mainly Gaussian pro file but the gradual addition of phosphorus transforms them to Lorentz ian-type curves. An attempt to approximate the histograms dV(p) = f(D( p)) with the minimum number of distribution curves made up of the corr esponding Gaussian and Lorentzian components indicates that each succe ssive addition of phosphorus creates a dominant new pore component at a larger pore diameter. At the same time, the components at smaller po re diameters are diminished and eventually disappear as more phosphoru s is added.