Catalyst performance testing state

Figure 2.2.1 shows the simplified sketch of the reactor used for the microactivity test. As can be seen, a fluid-bed catalyst is tested in a fixed bed reactor in the laboratory to predict its performance in a commercial fluid bed reactor. This can be done only because enormous empirical experience exists that has accumulated throughout several decades in several hundreds of reactors both in production and in laboratories. The standard states ... 

The effect of time averaging on yields in transient tests can be minimized by shortening the duration of the test. Also, a fixed bed test is superior to an FFB activity test in that backmixing is minimized. Furthermore, an isothermal fixed bed test would be easier to interpret than the adiabatic MAT test. This work shows that from the point of view of a catalyst characterization test, a small steady state riser will give the most direct information for catalyst performance in a commercial riser. 

Subsequent deployment of the new catalyst in the cathode layer of small-area MEAs first, then large-area MEAs, and finally fuel cell stacks represents the typical series of performance tests to check the practical viability of novel ORR electrocatalyst materials. Figure 3.3.15A shows the experimental cell voltage current density characteristics (compare to Figure 3.3.7) of three dealloyed Pt-M (M = Cu, Co, Ni) nanoparticle ORR cathode electrocatalysts compared to a state-of-the-art pure-Pt catalyst. At current densities above 0.25 A/cm2, the Co- and Ni-containing cathode catalysts perform comparably to the pure-Pt standard catalyst, even though the amount of noble metal inside the catalysts is lower than that of the pure-Pt catalyst by a factor of two to three. The dealloyed Pt-Cu catalyst is even superior to Pt at reduced metal loading. 

The activity of the catalysts was tested in the hydrogenation of crotonaldehyde, cinnamaldehyde and furfural at atmospheric pressure. Before the reaction, the catalysts were reduced in a stream of dihydrogen at 623 K. Hydrogenation reactions were carried out in a standard fixed bed vertical reactor. After the catalyst reduction, the reactor was cooled down to the reaction temperature (423, 470 or 523 K) and unsaturated aldehyde and hydrogen were introduced onto the top of the reactor. The first product sample for analysis was taken after 30 min of reaction (period needed to reach reaction steady state). The identification and analysis of the reaction mixtures were performed by means of GC-MS using HP-50 capillary column. 

Using the measured data for the coated 400 cpsi extruded ceramic and wrapped metal structures shown in Table 1 (1), the Heat Mass Transfer Factors are calculated to be 7.96/mm for the square and 7.68/mm2 for the sinusoidal channel structures. The difference between these two values is within the error associated with the assumptions of the analysis. These numbers suggests that the steady-state catalyst performance of these two structures, when tested under the same conditions, will be similar. 

Analysis of a set of catalyst performance data which represent a direct comparison between the 400 cpsi square and sinusoidal cell structures indicates almost identical steady-state performance for the catalysts on the two structures. These data suggest that the Heat Mass Transfer Factor can in fact be used to predict relative catalyst performance when other aspects of the experiment such as washcoat loading, substrate volume, and test conditions are held constant. 

However, the important criteria for WC to be implemented in fuel cells are its surface area, phase, and porosity. Ganesan and Lee reported that WC with a surface area of 170 m /g was obtained by thermal method, but the product tuned to be containing more sub-tungsten carbide (W2C) [70]. The latter was used to support Pt catalyst for methanol oxidation reaction. No test was done for ORR. Nevertheless, authors believed that oxide layer formed on carbide support is the key player in promoting alcohol oxidation by providing oxygen species as indicated by the decrease in desorption temperature of CO. In a different study carried out by the same group, mesoporous WC was synthesized and used as a support for Pt [71]. The mesoporosity was introduced by addition of surfactant like cetyltrimethylammonium bromide (CTABr). Catalyst performance was evaluated under identical conditions as previously stated however, no statement has been reported on ORR activity and electrochemical stability in both cases [70, 71]. 

Process simulations with time-varying catalyst activity were performed based on a quasi-steady-state approximation (Lababidi et al., 1998). The underlying principle is that because catalyst aging is a relatively slow process in the operating cycle timescale, it can be assumed that the process is stable during short periods of time. In this case, it is considered that this time period is equal to the duration of the mass-balance runs during the catalyst stability tests (12 h). The simulation runs start at t=0 with the catalyst in its fresh state = 1.0 for the entire catalyst length). The concentration and temperature profiles are established from the steady-state solution of the heat and mass balances, as described previously. The next step is to estimate the local amount of MOC from the axial metal profiles in this period and after that to evaluate the deactivation functions for each reaction. The time step is increased and all the calculations are repeated. 

The photocatalytic experiments were performed in a horizontal quartz tube which it have TiOi. Illumination was provided by 500 W mercury lamps, located above the horizontal quartz tube. The reactant was 0.1% (v/v) ethylene in air. In case of Photo-Catalyst test, reactor effluent samples were taken at 30 min intervals and analyzed by GC. The composition of hydrocarbons in the feed and product stream was analyzed by a Shimadzu GC14B (VZIO) gas chromatograph equipped with a flame ionization detector. In all case, steady state was reached within 3 h. 

In our first experiment we decided to test the conversion of sunflower oil into biodiesel (16). Treatment of sunflower oil (1) with NaOMe in MeOH results in formation of a mixtme of fatty acid methyl esters (FAME), also known as biodiesel, and glycerol (2) (Figme 4.3). The reaction was performed with a six-fold molar excess of methanol with respect to sunflower oil at elevated temperatures (60°C) using a basic catalyst (NaOMe, 1% w/w with respect to sunflower oil). The CCS was equipped with a heating jacket to ensure isothermal conditions. The sunflower oil was preheated to 60°C and was pumped at 12.6 ml/min into one entrance of the CCS. Subsequently, a solution of NaOMe in MeOH was introduced through the other entrance at a flow rate of 3.1 ml per minute. After about 40 minutes, the system reaches steady state and the FAME containing some residual sunflower oil is coming... 

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