Catalytic partial oxidation (CPO) of CH4 in air was investigated over Rh/Al2O3 catalysts (0.01, 0.05, 0.1 and 1 wt% Rh0) in co-feed modus in laboratory scale fixed-bed reactors. Main focus was on catalyst stability and selectivity at low temperatures (<700 °C). A particularly high selectivity to CO was observed, indicating existence of a direct pathway.

Catalytic partial oxidation (CPO) of methane has been investigated over Co/Al2O3 catalysts with different metal (0.1 wt.% of Ni, Pt, Rh, Ru or Pd) and oxide (< 4 wt.% Fe3O4/Cr2O3, La2O3, SnO2 or K2O) promoters. A comparison with Ni- and Fe-based catalysts was performed. Methane conversions and selectivities were determined in the temperature range 200-750 degrees C at atmospheric pressure in a continuous fixed-bed quartz reactor. The scope was to identify factors for control of product selectivity and investigate the potential of low temperature operation. The unpromoted 10 wt.% Co/Al2O3 catalyst showed stable steady-state performance at 650 degrees C in the gas hourly space velocity range 15-180 N I CH4/g(cat) h. Equilibrium behaviour was observed during ramping (-1 degrees C/min) until a sudden extinction occurred around 450 degrees C, seemingly coinciding with O-2 breakthrough. Addition of 0.1 wt.% metal promoter, particularly Pt and Rh, caused the activity to be maintained to lower temperatures. While Rh maintained H-2 formation, Pt promoted combustion at low temperatures. Addition of 0.1 wt.% Ni by co-impregnation promoted carbon formation and deactivation. Addition of surface oxides typically promoted instability, deactivation and combustion. While the performance of Ni catalysts was superior to Co catalysts at low temperatures, Fe-based catalysts showed combustion activity in the whole temperature range. A hydrogen yield according to equilibrium predictions seems to be the best possible achievement. (c) 2007 Elsevier B.V. All rights reserved.

DOSY has been extremely successful in many studies of molecular weight distributions, especially when the components are separable along the chemical shift axis. However, an unresolved NMR resonance yields the familiar problem of overlapping exponential decays. In a study of methylaluminoxane (MAO), a set of data processing and simulation tools were developed: read Bruker data files (Matlab); preliminary non-linear least-squares fit with f-test (Matlab); movie generation of the fits (Matlab); conversion of diffusion coefficients to molecular masses through molecular volumes (Gaussian-98); and simulation of DOSY data sets for various molecular mass distributions (Mathematica). These tools are presented here and briefly compared with other DOSY analysis methods.

The reaction between tBu6Al6O6 and AlMe3, as observed by Watanabi et al., does not contrast with our observation that no reaction occurs between commerical type methyl aluminoxane (MAO) and AlMe3, since the aluminoxane starting structures are different: Commercial MAO has Me/Al ≈ 1.5. The reactivity of MAO with AlMe3 is associated with release of strain in −Al−O−Al−O− four-membered rings, whereas acidity largely stems from the occurrence of −Al−Me−Al− bridges or three-coordinated aluminum.