Aluminophosphates Oxynitrides as Base Catalysts: Nature of the Base Sites and Their Catalytic Implications

By means of IR spectroscopy it has been found that Al–NH–P and P–NH2groups are formed during the high temperature NH3treatment of amorphous aluminophosphates (ALPONs). The amount of nitrogen incorporated increases with time of exposure to NH3, while also increasing the ratio of the more basic –NH– with respect to the less basic –NH2groups. This is reflected in the catalytic activities of these materials for the Knoevenagel condensation reaction using the activated methylenic groups of different pK a values as reactants. ALPON materials have stronger basic sites than alkaline exchanged Y zeolites and weaker basic sites than MgO and Hydrotalcites. However, in the case of Knoevenagel condensation reactions the ALPONs present a very adequate basicity, especially when the competing Michael addition can also occur. In such cases the selectivities of the oxynitrides are better that those showed by MgO and hydrotalcites.