Abstract
Laponite synthetic clay has been modified via exchange with "A112M7+" (M = Al, Ga, Fe or In) pillaring species and further exchanged after calcination with various metal species. The chemically tailored materials produced have been characterised using powder XRD, thermal analysis, N2 sorption at 77 K, FT-IR and MAS-NMR spectroscopies. Preliminary testing as to their suitability as deNOx catalysts has been carried out both through direct catalytic testing and in-situ FT-IR spectroscopy with NO sorbate. The pillaring species themselves were also investigated through precipitation of their sulphates and characterisation by powder XRD, as synthesised and after heating to 1150°C, thermal analysis and FT-IR and MAS-NMR spectroscopies. None of the "A112M7+ Keggin sulphates" (M = Al, Ga, Fe or In) were single phase materials, all containing the A1137+ Keggin sulphate and at least one other phase. The successful exchange and pillaring of the Laponite parent clay was demonstrated through 27Al MAS-NMR by the observation the of resonance assigned to tetrahedral AlO4. 29Si MAS-NMR showed the presence of both Q3 layer and Q2 edge Si sites and the emergence of a resonance corresponding to Q3 (1OH) Si sites upon exchange of the parent clay. Heating the exchanged material resulted in the disappearance of this resonance, but a further resonance was observed corresponding to Q4(1Al) Si sites, further confirming a successful pillaring reaction. N2 sorption at 77 K gave isotherms consistent with the presence of both micropores and mesopores and specific surface areas in the range 260 m2g-1<SBET<360 m2g-1, with Kelvin pore diameters between 35 and 39 A. Upon heating the exchanged clays, no major change in the specific surface area was observed up to 600 °C, with the Kelvin pore diameter reaching a maximum at 400 °C but maintaining at least its original value up to 700 °C. In-situ FT-IR spectroscopy of Co2+-exchanged "A112Fe7+" Laponite in the presence of NO revealed a number of surface species (most notably nitrates, N2O and NO2) and suggestions have been made as to their route of formation. Catalytic testing of a range of materials for N2O destruction in both the presence and absence of CH4 showed a number to achieve 100 % conversion at low reactant flow rates, with the V-exchanged A1137+ Laponite showing the highest potential as a deN2O catalyst.