Abstract
Isopropylation of MAPO-5 (M: Co and Ni) gave high selectivity for 4,4′-DIPB. 4-IPBP worked as a precursor of 4,4′- and 3,4′-DIPB; however, 3-IPBP was not concerned. 4,4′-DIPB was predominantly formed by exclusion of bulkier 3,4′-DIPB at their transition states through their steric interaction with channels of MAPO-5 with AFI topology.
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•Synthesis of APO-5 substituted with cobalt and nickel with AFI topology.•High selective formation of 4,4′-DIPB in the isopropylation of BP.•4-IPBP was a precursor of 4,4′-DIPB; however, 3-IPBP was not concerned.•Shape selective catalysis by restricted transition state selectivity mechanism.
The isopropylation of biphenyl (BP) was examined over transition metal substituted aluminophosphates (MAPO-5; M: Co and Ni) with 12-membered (12-MR) oxygen ring pore-entrances of AFI topology. The MAPO-5 samples were synthesized by dry gel conversion method using trimethylamine as a structure directing agent, and their properties were characterized by XRD, XPS, SEM, N2 adsorption, NH3-TPD, pyridine adsorption, and o-xylene uptake. They are clear crystals without impurity phases and agglomerates, and found small amounts of Brønsted acid sites which are expecting active for acid catalysis. The isopropylation of BP over both of Co(5)APO-5 and Ni(5)APO-5 at 250°C gave the high selectivities for 4,4′-DIPB: 65–75%. 4-IPBP is almost exclusive precursor of 4,4′- and 3,4′-DIPB. 3-IPBP was not significantly concerned even though 3-IPBP was predominant among IPBP isomers at the late stages: the MAPO-5 channels allow preferential access of 4-IPBP, and prevent the access of 3-IPBP due to reactant selectivity mechanism. The selective formation of 4,4′-DIPB occurred by preferential exclusion of bulkier 3,4′-DIPB and other isomers through the steric interaction of transition states with the channels by the restricted transition state selectivity mechanism. MAPO-5 (M: Co and Ni) has the same level of the selectivities for 4,4′-DIPB to SSZ-24 and other MAPO-5 (M: Si, Mg, and Zn), and these selectivities were originated by the AFI channels. The selectivities for 4,4′-DIPB were kept 65–75% at low and moderate temperatures over MAPO-5 (M: Co and Ni); however, they were decreased by the isomerization to stable 3,4′-DIPB with the increase in temperature.