Hypothesis, catalyst performance testing

This paper reports first results of research and development work to achieve nitrogen oxide reduction under lean diesel exhaust gas conditions. Much attention is paid to the influence of operation conditions on catalyst performance. A major part of the paper deals with the influence of the hydrocarbon component, the hydrocarbon concentration and the HC/NO ratio on the activity of a special developed platinum based catalyst. Other aspects discussed are a spectroscopic characterization and a selectivity study. A hypothesis of a "dual-site" reaction mechanism for NOx-reduction in lean diesel exhaust gas precious metal based catalyst is established. Finally, first promising results on the performance of the catalyst system in a vehicle dynamometer test are given. 

This hypothesis was tested by carrying out a kinetic study of the HKR of epichlorohydrin using Jacobsen Co(III)-salen catalyst with four different counterions, namely, acetate (OAc), tosylate (OTs), chloride (Cl) and iodide (I) (22). Approximately, 0.5 mol% loading of all the catalysts was used to perform the HKR of epichlorohydrin. As shown in Table 43.2, the ran initial rates with Co-OAc and Co-OTs salen catalysts were similar and slightly below those with Co-Cl and Co-I salen. Nevertheless, all of the catalysts were quite active initially. After conducting... 

Table 3. In order to test the hypothesis that heterogeneous catalyst is better than the homogeneous one, beeause the former allows improving the control over iron ions during the Fenton ehemistry, several consecutive degradations were performed with a fixed amount of eatalyst. Figure 19 shows the time needed for four consecutive batch degradations of 100 ml 50 mM Na2S04 (pH 2.8) + 0.06 mM RB5 + 10.7 mM H2O2 (twice of the stoiehiometrie amount required) + 0.1 g eatalyst Cl. At the end of each discoloration the solution was allowed to settle down into the reaetor and the solution was withdrawn carefully. Then, a fresh solution (100 ml 50 mM Na2S04 + 0.06 mM RB5 + 10.7 mM H2O2) was reloaded over the previous 0.1 g eatalyst Cl to start a new RB5 discoloration. The process was repeated three times.

As demonstrated throughout this volume, catalyst development is much more than just plant testing. Rejecting a hypothesis because of poor plant performance and not determining whether the catalyst was improperly prepared or treated can inhibit a breakthrough. Similarly, characterizing only the catalysts that give excellent performance so as to understand the system may cause researchers to miss the critical variable. 

This increased sensitivity is believed due to the fact that the onium salt produces a much stronger acid, in this case HSbF. Another contributing factor could be participation of free radicals, formed during irradiation of the onium salt. To test this hypothesis, experiments were performed with a latent UV-deblockable sulfonic acid. This compound produces both PTSA and free radicals when it is irradiated. Although the acid produced was PTSA, the curing result was consistent with the result from the onium salt experiment. These experiments indicates it is the free radicals which are effective in crosslinking the matrix. However, it may also just be a solubility effect, e.g. catalysts II and III may be simply more soluble in the MAGME-polymers than PTSA. Further experimentation is needed to determine whether it is a solubility effect or participation of free radicals that explains the low sensitivity of PTSA. In the experiments with pure PTSA, no increase in sensitivity was observed when the PTSA concentration was increased above 0.3J w/w. 

Keggin-type phosphomolybdates (POM s) were tested as catalysts for the selective oxidation of isobutane to methacrylic acid. Doping the POM with antimony improves the catalytic performance especially at isobutane-lean conditions, since a redox reaction between Sb " " and Mo leads to the development of a reduced POM which is stable even in an oxidizing environment, and which is more selective to methacrylic acid. Another important factor to control the reactivity is the pH of precipitation of the POM. When the preparation of the catalyst is carried out via the formation of a lacunary precursor, the time necessary to reach steady catalytic performance ( equilibration time ) is considerably less than that for POM s prepared conventionally at strongly acid pH. An hypothesis about the nature of the active sites is formulated. 

An important example of a hypothesis testing of the last-mentioned kind is the analysis of the influence of varying the values of individual input variables (e.g., catalyst components and their proportions) on the performance of a catalytic material by means of an approach called analysis of variance. The approach assumes that each output variable... 

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