Acidity and surface behaviour of alumina-boria catalysts studied by adsorption microcalorimetry of probe molecules

Acidity and basicity of alumina-boria catalysts supported on porous or non-porous alumina have been studied by adsorption microcalorimetry of probe molecules (ammonia, pyridine and sulphur dioxide). Despite decreasing in initial heats, the total acidity as determined by ammonia adsorption increased in number and strength as a function of percentage of boron oxide. Ammonia, as a strong base, was shown to cover all types sites from strong to weak acid sites. Pyridine, as a weaker probe, was shown to dose only the stronger sites of the samples which stay nearly constant after B₂O₃ coverage approaching the monolayer. The basic sites of the amphoteric alumina support are neutralized by 10 wt% of boron oxide on non-porous alumina and 20 wt% of B₂O₃ on porous alumina. The catalytic activity for partial oxidation of ethane increased with acidity and reached a maximum constant value above 20 wt% of boron oxide.