The physical and catalytic properties of aluminum-boron-phosphorus-oxygen solids

Phosphate solids containing varying ratios of phosphorus, aluminum, and/or boron were prepared and characterized. They had surface areas ranging from 4 to 350 m{dollar}sp2{dollar}/g contained predominantly in mesopores of 10-50 A radii. Excess aluminum Al-B-P-O compositions contained micropores as well.; The Al-B-P-O solids were primarily amorphous with crystalline regions of either BPO{dollar}sb4,{dollar} AlPO{dollar}sb4,{dollar} or both. B-P-O and Al-P-O were more crystalline, containing BPO{dollar}sb4{dollar} and {dollar}rm Bsb2Osb3{dollar} or different AlPO{dollar}sb4{dollar} phases and {dollar}rm Psb2Osb3,{dollar} respectively. The increasingly amorphous nature of the solids resulted in increasing surface area. The solids were thermally stable up to 1000{dollar}spcirc{dollar}C although large quantities of H{dollar}sb2{dollar}O evolved from the solids over a range of temperatures. The acidic sites present were of varying strengths whose distribution was noted to shift towards weaker acids with increasing aluminum content.; The catalytic nature of the solids was investigated primarily with 2-methylbutanal. The reaction produced predominately isoprene, 2-methyl-2-butene, 2-methyl-1-butene, and 3-methyl-2-butanone, which were believed to be the primary products. Isoprene formation appeared to proceed via a different mechanism than the methylbutenes and 3-methyl-2-butanone. The presence of water, due to the dehydration process, played an important role in the catalytic behaviour of the solids, either through formation of acid sites or intermediate species, blockage of the active sites, or by alteration of the physical properties of the solids.; The initial catalytic behaviour and activity of the solids have been correlated with the physical properties. Surface area appeared to strongly influence the activity. Low mass balances were noted and correlated with low selectivity to isoprene. Irreversible chemisorption of a species with the surface appeared to occur, possibly through an alkene functionality. The acid strength appeared to correlate with catalytic behaviour. The presence of strong acid sites in the excess boron compositions resulted in higher activity and low mass balance. As site strength shifted to predominantly weaker sites, activity was reduced and mass balance improved. Irreversible chemisorption appeared related to the presence of stronger sites.