Nickel Amine Complexes as Structure-Directing Agents for Aluminophosphate Molecular Sieves: A New Route to Supported Nickel Catalysts

Abstract

Open framework aluminophosphates (AlPOs) with the framework types CHA, AFI, AEI, SAS and SAV have been prepared using nickel complexes of linear and macrocyclic polyamines as structure-directing agents: The [Ni(diethylenetriamine)₂]²⁺ complex has been used to prepare aluminophosphate-fluoride versions of the CHA and AFI topologies as well as substituted metalloaluminophosphates (MAPOs) and silicoaluminophosphates (SAPOs) with the CHA topology; the nickel complex of the macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) acts as a structure-directing agent for MAPO-18 (AEI topology), and the nickel complexes of 1,4,8,11-tetraazacyclotetradecane (cyclam) and 1,4,8,11-tetramethylcyclam direct the formation of STA-6 (SAS topology) or STA-7 (SAV topology) depending on the inorganic composition and the type of amine added as a cobase to control the synthesis pH. Magnesioaluminophosphate-5 (AFI topology) containing complexed nickel has been prepared using a novel mixed azamacrocycle-quinuclidinium cation as a structure-directing agent. Nickel complex-containing AlPOs and SAPOs with the CHA framework topology have been calcined and used as catalysts for the conversion of butane over the temperature range 375 – 575°C with a WHSV of 1.8 h^-1. The inclusion of nickel increases the rate of conversion and also changes the composition of the products from the full C1–C4 range to pure methane. This behavior is attributed to the reduction of Ni(II) to finely dispersed supported nickel particles.