Structural and mechanistic investigation of a phosphate-modified HZSM-5 catalyst for methanol conversion

Phosphorus modification of a HZSM-5 (MFI) zeolite by wet impregnation has long been known to decrease aromatic formation in methanol conversion chemistry. We prepared and studied a catalyst modified by introducing trimethylphosphine under reaction conditions followed by oxidation. Magic-angle spinning (MAS) NMR shows that extensive dealumination occurs, resulting in a catalyst with a much higher framework SiO2/Al2O3 ratio, as well as extraframework aluminum and approximately 1.4 equiv of entrained phosphoric acid (under working conditions) per aluminum. Upon dehydration or regeneration, the phosphoric acid is converted, reversibly, to entrained P4O10. The aromatic selectivity of the modified catalyst is significantly lower than that of an unmodified zeolite with a similar, increased framework SiO2/Al2O3 ratio. By comparing the rates of H/D exchange in propene under conditions similar to those in methanol conversion chemistry, we determined that the acid site strength is indistinguishable on modified and unmodified zeolites, and this is consistent with theoretical modeling. On the phosphorus-modified zeolite, the rate of propene oligomerization is greatly suppressed, suggesting that entrained phosphate is an impediment to sterically demanding reactions.     

Porous Polymers by Emulsion Templating

Highly porous and permeable polymers are produced by polymerisation of the continuous phase of high internal phase emulsions (HIPEs). The morphology and properties of the resulting PolyHIPE materials can be varied, allowing the materials to be optimised for a variety of applications. Void diameter is controlled from 1 to around 100 μm by altering the HIPE stability. Surface areas greater than 700 m²g⁻¹ can be achieved by replacing some of the monomer phase with non-polymerisable solvent, in conjunction with a high crosslink density and the use of a surfactant mixture that limits Ostwald ripening. PolyHIPEs can be produced in a variety of physical forms including large monolithic slabs, rods and flat relatively thin membranes. The materials are currently under investigation for use as electrochemical sensor membrane substrates and as porous matrices for cell culture.     

Polarisation parameters in positive pion photoproduction

Measurements have been made of the polarisation parameters Σ, T and P for the process γp → π⁺n in the photon energy range 520–2250 MeV at c.m. angles between 30° and 120°. These data were obtained in a double polarisation experiment, using the polarised photon beam from the Daresbury electron synchrotron incident on a polarised proton target. The data are compared with predictions from current theoretical analyses.     

Albert Cyril Offord, Frs, 1906-2000

Cyril Offord was one of the most distinguished and certainlythe most senior of British mathematical analysts. With J. E.Littlewood, he pioneered the subject of probabilistic analysisby studying the typical behaviour of the zeros of a random polynomialwith real coefficients, or an entire function.     

Synthesis of enantiomerically pure tertiary 1,2-aminoalcohols by the highly diastereoselective reductive ring opening of oxazolidines

A number of enantiomerically pure 1,2-aminoalcohols containing tertiary nitrogen atoms bearing chiral substituents have been prepared by highly diastereoselective reductive ring cleavage of oxazolidines derived from ketones and pseudoephedrine or ephedrine. The ring cleavage occurs with retention of configuration.