Gravimetric vapour sorption

INVESTIGATION OF THE ACID-BASE PROPERTIES OF AN MCM-SUPPORTED RUTHENIUM OXIDE CATALYST BY INVERSE GAS CHROMATOGRAPHY AND DYNAMIC GRAVIMETRIC VAPOUR SORPTION... 

Dynamic vapour phase techniques are interesting tools for the determination of these properties. When compared to standard wettability experiments, they provide two main benefits. They can easily and reproducibly be applied to powders and a wide variety of probe molecules can be selected. In the current study dynamic gravimetric vapour sorption (DVS) and inverse gas chromatography (IGC) have been used to characterise the energetic and acid-base properties of a calcined ruthenium oxide / MCM41 catalyst as well as the corresponding MCM41 support. 

Dynamic gravimetric vapour sorption involves the use of an ultra-sensitive microbalance. The solid sample is placed in the sample pan at the end of the hang-down wire while the probe molecule is vaporised in an inert carrier gas stream. Adsorption of vapour is measured as a gain of weight, desorption as a loss of weight. From these changes of weight at different vapour concentrations sorption isotherms can be determined. 

A Ruthenium oxide / MCM41 catalyst as well as the pure MCM41 support were studied by inverse gas chromatography and dynamic gravimetric vapour sorption. The obtained... 

Gravimetric vapour sorption analysis Raman spectroscopy X-ray diffraction Intrinsic solubility Isothermal microcalorimetry... 

Vapour and gas sorption measurements can be performed with static or dynamic methods, either of which can provide information on equilibrium behaviour. Furthermore, the measurements can be performed using gravimetric or volumetric based instrumentation. The most common flow methods are inverse gas chromatography (IGC) [1] for volumetric studies and dynamic gravimetric instrumentation [2]. 

In the sorption experiments, a polymeric sample is suspended to a quartz spring balance, having a measured extension, in a vacuum chamber. A vapour or a gas is then introduced and maintained at a constant pressure. The gas or vapour dissolves and diffuses into the polymer and the weight gain is gravimetrically measured. The analysis is focused on the initial part of the mass-gain curves. 

Permeability is so low that, in sorption experiments, large pressure differences and membranes of small thickness have to be employed. These restraints do not apply to condensable vapours or highly permeant gas. In the last case, relaxation processes in the polymer matrix cause changes in the transport behaviour and make the permeability time-dependent. In contrast, only vapours of sufficiently high solubiUty are suitable for the gravimetric measurements used in the sorption experiments. Consequently, there are only few systems for which both sorption and permeation results have been reported. Low et al. conducted the two types of moisture transport experiments on a polyamide 6/elay nanocomposite. The authors found that the activation energy of moisture permeation obtained from the sorption experiment is lower than that derived from the permeation measurement. They concluded that the interaction and contribution of the diffusion and solubility parameters show complex transport behaviour in these nanocomposite films. 

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