Microwave-assisted synthesis and characterization of Cu-containing AlPO4-5 and SAPO-5

The microwave-assisted hydrothermal synthesis of Cu-containing AFI structures AlPO4-5 and SAPO-5 in good product quality was successfully accomplished. The modification of texture, acidity and redox properties caused by incorporation of Cu was examined using XRD, SEM, TG/DTA, N2 adsorption, UV–vis- and FTIR spectroscopy. Copper impregnated AlPO4-5 and SAPO-5 served as reference samples. Pyridine and CO were used as probe molecules to characterize acidity and nature of Cu species. XRD patterns of the calcined, template-free samples confirmed the crystallinity and the absence of any crystalline copper phase (Cu, Cu2O, CuO). Surface areas and pore volumes indicate the absence of pore blocking by amorphous material or agglomerated Cu species. Brønsted acid sites were created in CuAPO-5 confirming isomorphous substitution of Cu2+ into the lattice. Cu2+/Cu+ with Lewis acid character could be identified by FTIR spectroscopy using pyridine as probe molecule. Pre-reduction with CO and H2 at various temperatures allowed a differentiation of Cu sites. An essential part of the Cu is located on non-lattice positions with high dispersion in form of isolated Cu2+. Reduction with CO revealed the existence of Cu2+ sites bearing oxygen (e.g., Cu2+–O–Cu2+). Reduction with H2 and subsequent CO adsorption leads to Cu aquacarbonyls.