High-resolution ac calorimetry was used to measure the heat capacity of n-hexyl-4'-npentyloxybiphenyl-4-carboxylate in the vicinity of the smectic-A (SmA)hexatic-8 and hexatic-8 -E transitions. The Smdhexatic-8 transition was found to be continuous with critical exponents u =n+ =0.61+0. 02 and amplitude ratio 3 + /2 =0.84+0.03. The addition of a crystalline-B material [N-(4-n-butyloxybenzylidene)-4-octylaniline (40.8), 10 wt. %] produced a weakly-first-order SmAhexatic-8 phase transition. The data with~T -T,~) 100 mK can be fitted by a power law with +=0.49+0.02 and A+/A =-0.82+0.03. The large values for the critical exponents and the theoretical suggestion that the Sm Ahexatic-B transition may be near tricritical point (u, =O.S) are discussed. The hexatic-8 -E transition was found to be first order in nature.
The catalytic action of Mo 2 N and Au/Mo 2 N has been assessed in the selective gas phase hydrogenation of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN). The nitrides were synthesised via temperature programmed treatment of MoO 3 in H 2 ? N 2 and Au introduced by deposition-precipitation with urea. We have examined the influence of nitride crystallographic phase (tetragonal b-Mo 2 N vs. cubic c-Mo 2 N) and surface area (7-66 m 2 g-1) on the catalytic response. Catalyst activation by temperature programmed reduction has been monitored and the reduced catalysts characterised in terms of BET area/pore volume, H 2 chemisorption/temperature programmed desorption (TPD), powder X-ray diffraction (XRD), elemental analysis, scanning (SEM) and transmission (TEM) electron microscopy and X-ray photoelectron spectroscopy (XPS) measurements. The formation of band c-Mo 2 N was confirmed by XRD and TEM. c-Mo 2 N exhibits a platelet morphology whereas b-Mo 2 N is characterised by an aggregation of small crystallites. Hydrogen chemisorption and TPD analysis have established a greater hydrogen uptake capacity (per unit area) for b-Mo 2 N relative to c-Mo 2 N, which is associated with surface nitrogen deficiency, i.e. higher surface Mo/N for b-Mo 2 N. Incorporation of Au on both nitrides resulted in an increase in surface hydrogen. The Au phase takes the form of nanoscale particles with a mean size of 7 and 4 nm on b-Mo 2 N and c-Mo 2 N, respectively. Both b-Mo 2 N and c-Mo 2 N promoted the exclusive hydrogenation of p-CNB to p-CAN where the b-form delivered a higher specific (per m 2) rate; the specific rate for c-Mo 2 N was independent of surface area. The inclusion of Au on both nitrides served to enhance p-CAN production.
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