Ammonia mobility in chabazite: insight into the diffusion component of the NH3-SCR process.

The diffusion of ammonia in commercial NH3-SCR catalyst Cu-CHA was measured and compared with H-CHA using quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulations to assess the effect of counterion presence on NH3 mobility in automotive emission control relevant zeolite catalysts. QENS experiments observed jump diffusion with a jump distance of 3 Å, giving similar self-diffusion coefficient measurements for both Cu- and H-CHA samples, in the range of ca. 5-10 × 10(-10) m(2) s(-1) over the measured temperature range.

Improving sensitivity and accuracy of pore structural characterisation using scanning curves in integrated gas sorption and mercury porosimetry experiments.

Gas sorption scanning curves are increasingly used as a means to supplement the pore structural information implicit in boundary adsorption and desorption isotherms to obtain more detailed pore space descriptors for disordered solids. However, co-operative adsorption phenomena set fundamental limits to the level of information that conventional scanning curve experiments can deliver. In this work, we use the novel integrated gas sorption and mercury porosimetry technique to show that crossing scanning curves are obtained for some through ink-bottle pores within a disordered solid, thence demonstrating that their shielded pore bodies are undetectable using conventional scanning experiments.

NMR studies of cooperative effects in adsorption.

The conversion of gas adsorption isotherms into pore size distributions generally relies upon the assumption of thermodynamically independent pores. Hence, pore-pore cooperative adsorption effects, which might result in a significantly skewed pore size distribution, are neglected. In this work, cooperative adsorption effects in water adsorption on a real, amorphous, mesoporous silica material have been studied using magnetic resonance imaging (MRI) and pulsed-gradient stimulated-echo (PGSE) NMR techniques.