Catalysts experiment

The bed of parallel plates coated with Raney nickel catalyst was much more reactive than the bed of precipitated nickel. This was revealed by the generally lower CO concentration in the product gas during operation with the parallel plate bed for example, after 450 hrs stream time, it was 0.01% with the bed of sprayed Raney nickel (experiment HGR-14) and 0.05% with the bed of precipitated nickel catalyst (experiment HGR-13). 

Water present in the monomer solution before the addition of perchloric acid did not affect the rate of polymerisation (Experiment SGP6, Table 1), but if water was added to the catalyst solution before the polymerisation, with consequent formation of HC104, H20, which is insoluble in methylene dichloride, only the anhydrous acid was found to be an active catalyst (Experiment SGP7, Table 1). 

To clarify the mechanism by which gasoline composition is changed (reduction in concentration of the paraffins and an increase in concentration of olefins and aromatics) by ZSM-5 in the dual zeolite catalyst, experiments were carried out on catalysts containing only ZSM-5 dispersed in the matrix. The catalyst containing 1 Wt.% ZSM-5 was used in order to duplicate the concentration of ZSM-5 in the dual zeolite catalyst studied earlier. Experiments with the pure matrix catalyst were used to define the contribution of ZSM-5. 

TTNs). In the case of slow homogeneous chemical catalysts, the [S]/[C] ratio can even be unity (i.e., stoichiometric conditions). The numerical values for the total turnover number and the turnover number are driven apart by the average number of recycles a catalyst experiences. In the limit of no recycle, the values are identical (TTN = TON). Whereas recycling is very important in biocatalysis, it is apparently not high on the agenda in chemical asymmetric catalysis (Blaser, 2001). 

Figure 6. Effect of H2foil ratio on the coke content of the catalyst. Experiment Feedstock Kuwait VGO, catalyst NiV/SiOj, temperature 450 C1 pressure 30 bar, WHSV 2.2 kg/(kg-h), run length 200 h.

Supported Cobalt Catalysts. Experiments were conducted with [Co(PC)]/Si02 at 340°C to determine the important variables for the catalysis of a typical [M(PC)]. Table IV gives the results for runs which were conducted for varying periods of time. It is seen that even at 100 hr. the conversion only reached 36%. The equilibrium conversion at 342°C can be estimated to be 97%. (9) Thus, the reaction is quite far from equilibrium even at long times. This may be taken as evidence for product inhibition of the catalysis. This might be expected since tetrahydroquinoline is a stronger Lewis base than quinoline. Thus, the product could bind to the metal center and prevent activation of the substrate and/or hydrogen. One important conclusion is that the reaction is not over in 24 hours and it can be assumed that the difference in conversions noted in Table I with different [M(PC)] are due to differences in inherent activity of the [M(PC)]. 

The data from our catalyst experiment are balanced , i.e. there are exactly equal numbers of replicates for each catalyst. This is not a requirement for the one-way ANOVA and, if a small amount of data loss occurs, the analysis can still go ahead. For any given number of observations, the power of the ANOVA will be greatest with a balanced data set and this is also true for Tukey s test. The only circumstance where power will be greater with an imbalanced data set is where a Dunnett s test is planned. Here, the control group is of special importance because it is used in all the comparisons. For this test, it is worthwhile trying to generate some extra data for the control group. 

The correlation of spectroscopic data between model and real catalysts has always been a concern in catalyst characterization. Weiher et al. (2005) tried to address this issue with a cell design that was compatible with both model catalysts (e.g., submonolayer amounts of metals deposited on a silicon wafer) and real catalysts such as high-surface-area supported metals. Moreover, they also wished to have a design in which plug-flow conditions existed for the powder catalyst experiments. 

Fig. 17.9 Durability of solar disinfection without catalyst experiment of Fig. 17.7a, September 25th (a). Durability of solar disinfection with catalyst experiment of September 27th, 2003 (b). Initial and final samples were incubated for 24 h in the dark...

Stability of Various Catalysts. Experiments were conducted to investigate deactivation of the various catalysts. The conversion of light naphtha is defined here by the following equation ... 

Mechanochemistry has been proposed as an activation method [141-146]. This involves milling the catalyst precursor in a solvent, usually ethanol, prior to its conversion to the active catalyst. Experiments have shown that this procedure promotes the exposure of the (100) plane in the catalyst, which is considered to be the active crystal face [141-143, 146], and can reduce the particle size thus increasing the surface area [141,144—146]. Experiments with promoters show that this procedure gives more active and selective catalysts than those prepared by either chemical means or mechanical mixing [93, 141, 146]. 

A one-step synthesis with a good yield has been reported in which the conditions are mild, with Et4NBr as catalyst. Experiments on Cu and Ni catalysts with labeled compounds proved that the Cu-catalyzed reaction takes place with retention. Work has also been carried out on the kinetics of carbonate formation. ... 

S. R. Murff, E.A. Carlisle, P. Dufresne and H. Rabehasaina, "The Sulficat Presulfided Catalyst Experience", Am. Chem. Soc. Denver Meeting, 1993. 

The last point concerns the question of permanent involvement by the catalyst. Ideally, the catalyst is unchanged by the reaction. In practice this is not true. Since it is itself a reacting substance, the catalyst suffers from irrevcfsible chemical and physical changes, which decrease its ability to perform. Within the time frame of the reacting molecules, these changes are small. But as the process time continues and the catalyst experiences many billions of these events, deactivation becomes significant. ... 

In this chapter we have presented and reviewed the extensive body of work that neutron vibrational spectroscopy applied to catalysis represents. It is one of the largest, most important and influential bodies of neutron work to appear in the literature and much of the original work remains of considerable interest. This is partly because catalyst experiments are difficult to perform and require considerable commitment of neutron time and other resources. 

The vapor phase synthesis of methacrylic acid from propionic acid and formaldehyde was studied [42]. In particular, the choice of alkali metal cation and loading were evaluated for their effect on the activity and selectivity of silica supported catalysts. Experiments were carried out in 0.5 in. (o.d.) quartz reactors equipped with 0.125 in. thermowells. Alkali metal cations supported on silica are effective base catalysts for the production of methacrylic acid. Silica surfaces exchanged with alkali metal cations are capable of chemisorbing propionic acid yielding surface-bound silyl propionate esters and metal propionate salts. The alkali metal cation influences the temperature at which desorption of the ester occurs (Cs < Na < Li < support). For silica catalysts of equimolar cation loading, activity and selectivity to methacrylic acid show the opposite trend, Cs > K. > Na > Li. Methacrylic acid selectivity reaches a maximum at intermediate cation loadings where interaction of adjacent silyl esters is minimized [42]. 

---