Quantification of surface species present on a nickel/alumina methane reforming catalyst

Abstract

An alumina-supported nickel catalyst has been used to effect the 'dry' reforming of methane, using CO 2 as the oxidant. After 6 hours on-stream, reaction was stopped and the sample analysed by inelastic neutron scattering (INS). The INS spectrum reveals the presence of hydrocarbonaceous species as well as hydroxyl species present at the catalyst surface. Through the use of appropriate reference compounds, calibration procedures have been developed to determine the concentration of the retained hydrocarbon and hydroxyl moieties. Ancillary temperature programmed oxidation experiments establish the total carbon content. This approach not only enables the extent of overall carbon laydown to be determined but it also identifies the degree to which hydrogen is associated with carbon and oxygen atoms. The methodology described is generic and should be applicable to a wide number of heterogeneously catalysed systems.

Characterisation of hydrocarbonaceous overlayers important in metal-catalysed selective hydrogenation reactions

“…A feature assigned to hydroxyls on the alumina [11,12] is apparent, however, there is only a barely discernible feature (signal-to-noise ratio ~2) at 2970 cm -1 in the region where a hydrocarbon signature would occur.…”

“…Thus the overlayer is essentially aliphatic in nature. This is distinctly different from the hydrocarbonaceous layer present on a Ni/Al 2 O 3 methane reforming catalyst that has a C:H ratio in the range 160:1 to 2550:1 depending on the catalyst materials and preparation conditions [11,12].…”

“…As noted earlier, we have shown that it is possible to quantify the hydrogen present on a catalyst by INS [11,12]. Figure 6 shows the INS spectrum of 0.5933 gm of polystyrene and the difference spectrum from 23.2 gm of catalyst in the beam.…”

“…We have recently shown that vibrational spectroscopy with neutrons (inelastic neutron scattering, INS) is able to detect, speciate and quantify hydrogen in carbon deposited on nickel-alumina catalysts during methane reforming [10][11][12]. In the present paper we extend the methodology to investigate whether it is possible to better characterise the form of the hydrogen present in the hydrocarbonaceous overlayer that is an integral part of alkyne hydrogenation using supported metal catalysts.…”

“…Figure 6 shows the INS spectrum of 0.5933 gm of polystyrene and the difference spectrum from 23.2 gm of catalyst in the beam. Using the methods described elsewhere [11,12] we calculate that there are 1.2 -1. Table 1 and combining the data, allows us to deduce a C:H ratio of 1:1.8 -2.4.…”