CZC through the long-term stability and suppressing of the carbon dioxide production

As previously mentioned, the sample masses were adjusted to provide the same Cu content. For this reason, the mass of CZC5 considerably exceeded those of the other samples, and this may accounted for the amount of CO detected for CZC5 being substantially higher than those for the samples with higher Cu contents. In addition, after five days of pronounced decrease the carbon monoxide levels stabilized and did not exhibit any significant difference. This finding is consistent with the results of N₂O decomposition, indicating that the active Cu contents of these samples were very similar.

Here, it may be concluded that from Figure 2 and 3, the increase in Cu content from 5 to 15 percent has a beneficial effect on the catalytic performance of CZC through the long-term stability and suppressing of the carbon dioxide production. Further observations were that increase of the Cu loading proved to be less important for the stability of the catalyst although it had a beneficial consequence of low carbon monoxide production. However, the carbon monoxide production depends on the conversion of methanol as the activity order of the CZC samples is in correlation with the order of the CO levels throughout the entire time on stream (Figure 3). Accordingly, under the present experimental conditions, the samples with increased Cu contents may be regarded as more efficient catalysts for SRM, with respect to the formation of CO in particular. Considering that the CZC catalysts are porous materials and the methanol conversions in Figure 2 displayed no systematic variation with either the Cu loading or the Cu⁰ surface area, the effect of mass transport limitations on the catalytic performance was additionally investigated.

Since the CZC samples were not uniform in size as previously observed, thus each material three fractions with different particle diameters could be obtained by sieving method. Moreover, a Cu/CeO2 sample containing 25% of Cu, prepared by the same method, was found to slightly deteriorate during SRM, as a small amount of the original catalyst beads (3.3%) was transformed into a fine powder after reaction. On the other hand, the Zr-containing beads of the CZC samples remained essentially unchanged after catalytic investigations, which confirm that ZrO_2 is an important structural stabilizer.