Testing Catalysts

Industrial catalysts must conform to a strict specification and physical and chemical properties are measured at all stages of production. The tests most often included in catalyst specifications are listed in Table 1.7. 

The mechanistic aspects of zeolite-catalyzed reactions are discussed briefly in Chapter 9. 

The only way to know if a material acts as a catalyst is to test it in a reaction. Determining the activity of a catalyst is not as straightforward as it may seem. Particularly when working with single crystals and model systems, there are several pit falls. For example, we prefer to measure the activity in the limit of zero conversion, to avoid results that are influenced by thermodynamic constraints, such as limitations due to equilibrium between reactants and products. We also want data under conditions of known gas composition and accurate temperature. This may become problematic 

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Ion implantation has also been used for the creation of novel catalyticaHy active materials. Ruthenium oxide is used as an electrode for chlorine production because of its superior corrosion resistance. Platinum was implanted in mthenium oxide and the performance of the catalyst tested with respect to the oxidation of formic acid and methanol (fuel ceU reactions) (131). The implantation of platinum produced of which a catalyticaHy active electrode, the performance of which is superior to both pure and smooth platinum. It also has good long-term stabiHty. The most interesting finding, however, is the complete inactivity of the electrode for the methanol oxidation. 

Haber and co-workers worked out methods of catalyst testing and process development that are essentially the methods of choice today (6,7). 

Bosch and co-workers devised laboratory reactors to operate at high pressure and temperature in a recycle mode. These test reactors had the essential characteristics of potential industrial reactors and were used by Mittasch and co-workers to screen some 20,000 samples as candidate catalysts. The results led to the identification of an iron-containing mineral that is similar to today s industrial catalysts. The researchers recognized the need for porous catalytic materials and materials with more than one component, today identified as the support, the catalyticaHy active component, and the promoter. Today s technology for catalyst testing has become more efficient because much of the test equipment is automated, and the analysis of products and catalysts is much faster and more accurate. 

Catalyst testing and evaluation have been revolutionized by computers, automated test reactors, and analytical methods. With modem equipment, researchers can systematically prepare and screen many catalysts in a short time and efftciendy deterrnine, not only the initial catalytic activity and selectivity, but also the stabiUty and the appearance of trace products that may indicate some new catalytic properties worthy of further development. 

In the case of exothermic reactions, underestimating the transfer coefficients makes the real gradients less than the estimated ones. As such, this makes our estimates conservative, in the sense that if a criterion calls gradients negligible then they surely are. The intent here is to do most of the kinetic study and catalyst testing at gradientless conditions and this book will make use of the Colburn-type correlations as developed by Hougen (1951) and his associates. 

The operational characteristics of the older Berty reactors are described in Berty (1974), and their use in catalyst testing in Berty (1979). Typical uses for ethylene oxide catalyst testing are described in Bhasin (1980). Internal recycle reactors are easy to run with minimum control or automation. 

The experimental unit, shown on the previous page, is the simplest assembly that can be used for high-pressure kinetic studies and catalyst testing. The experimental method is measurement of the rate of reaction in a CSTR (Continuous Stirred Tank Reactor) by a steady-state method. 

From the heat generation alone the maximum tolerable temperature difference between catalyst and gas can be evaluated, as will be shown in a later chapter. This is never done in pollution control catalyst testing. Due to the simple conditions at very low concentration, the Ignition Curve can be evaluated for first order kinetics. 

The reaction was carried out in excess of the acid chloride with cooling and gave yields of 55-80%. Of the catalysts tested, stannic chloride gave the best results. ... 

Upson, L. L., What FCC Catalyst Tests Show, Hydrocarbon Prod November 1981, pp. 253-258. 

Laboratory catalyst testing is sometimes done under conditions that are far removed from exhaust gas conditions, and can be a very unreliable guide to the utility of a catalyst. For instance, noble metals may rank below base metal oxides in oxidation activity at low temperatures, but the ranking reverses at high temperatures. These and other hazards were pointed out by Schlatter et al. (53). Laboratory catalyst testing is usually done by the catalyst manufacturers, resulting in the rejection of a vast majority of formulations. 

Of the various Lewis acid catalysts tested, SnCl4 gave the highest diastereoselective product formation with predominance for the antz-diastereoisomer. This azztz-selectivity can be rationalized by invoking the Cram chelation model. 

In general, NO and NO2 are mutually beneficial for NOx reduction over the SCR catalysts tested. That is, the presence of NO enhances the NO2 conversion, and vice versa. This results in the synergistic effects of NO and NO2 in the catalytic reduction of NOx with NH3 over CuZSMS, FeZSMS and V20s/Ti02 catalysts. 

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. 

As illustrated in Fig. 1, the activated carbon displays the highest conversion and selectivity among all the catalysts during the initial reaction period, however, its catalytic activity continues to decrease during the reaction, which is probably caused by coke deposition in the micropores. By contrast, the reaction over the CNF composites treated in air and HN03 can reach a pseudo-steady state after about 200 min. Similiar transient state is also observed on the CNFs and the untreated composite. Table 3 collects the kinetic results after 300 min on stream over catalysts tested for the ODE, in which the activity is referred to the BET surface area. The air-treated composite gives the highest conversion and styrene selectivity at steady state. 

It is beyond the scope of this book to go though all the specifics of catalyst testing and to discuss all pitfalls that may arise. Instead we list the Ten Commandments for the Testing of Catalysts. This is a set of guidelines that have been provided by experts of a company called Catalytica [F.M. Dautzenberg in Characterization of Catalyst Development An Iterative Approach (Eds. S.A. Bradley, M.J. Gattuso, R.J. Ber-tolacini), ACS Symposium Series, Vol. 411 (1989)]. 

Reaction conditions 0.1 g of the zeolite Y modified catalyst, tested in a conventional glass microreactor with racemic butan-2-ol (7.35 x 10" mol h-1), prevaporized in a nitrogen diluent (6.2 -6.7 x 10" mol h-1). Products were analyzed using on-line GC with a 40m capillary y- cyclodextrin colimm with trifluoroacetyl stationary phase, temperature programmed from 25-70 "C with a split ratio of 120 1. 

The catalyst testing was carried out in a gas phase downflow stainless steel tubular reactor with on-line gas analysis using a Model 5890 Hewlett-Packard gas chromatograph (GC) equipped with heated in-line automated Valeo sampling valves and a CP-sD 5 or CP-sil 13 capillary WCOT colunm. GC/MS analyses of condensable products, especially with respect to O-isotopic distribution, was also carried out using a CP-sil 13 capillary column. For analysis of chiral compounds, a Chirasil-CD capillary fused silica column was employed. 

These experiments demonstrate that the surface-catalyzed 2 reaction is far more effident than either the or C pathway for the dehydrative coupling of alcohols over the solid add catalysts tested. High selectivity to configurationally inverted chiral ethers ensues, espedally in the case of the HZSM-5 catalyst, in which the minor C or C paths were further suppressed by "bottling" of 3-ethoxypentane by the narrow zeolite chaimels. 

Figure 1.9 Hybrid, multi-scale micro-reactor plant for catalyst testing for propane steam reforming [15],...

One implication of micro reactors on chemical-process engineering concerns the shrinkage of the total system. This is exemplarily discussed for catalyst testing. 

For catalyst testing, conventional small tubular reactors are commonly employed today [2]. However, although the reactors are small, this is not the case for their environment. Large panels of complex fluidic handling manifolds, containment vessels, and extended analytical equipment encompass the tube reactors. Detection is often the bottleneck, since it is still performed in a serial fashion. To overcome this situation, there is the vision, ultimately, to develop PC-card-sized chip systems with integrated microfluidic, sensor, control, and reaction components [2]. The advantages are less space, reduced waste, and fewer utilities. 

Jensen gives several examples for his present highly integrated chip systems [101], including a gas-phase reactor, a liquid-phase reactor, a catalyst-testing reactor, and a packed-bed multi-phase reactor. In addition, he provides the vision of a multiple micro-reactor test station (see Section 1.5.5.2). 

Shoebox-sized lab-on-a-chip laboratories personal dmg manufacture general advantages of micro flow Merck s production nitrations HTS parallel catalyst testing turnkey bench-scale test station standardization cube-like modules [210],... 

Process Miniaturization Second International Conference, CATTECH, December 1998 Steep progress in microelectronics in the past key players topics of IMRET 2 general advantages of micro flow energy, safety, process development, combinatorial catalyst testing, lab-on-a-chip biological applications anodically oxidized catalyst supports as alternatives to non-porous supports [220]. 

The corresponding scientific investigations have advanced considerably in recent years. Together with the field of catalyst testing and screening (see Section... 

Ajmera, S. K., Deiattre, C., Schmidt, M. A., Jensen, K. F., Microfabricated cross-flow chemical reactor for catalyst testing. Sens. Actuators 82, 2-3 (2002) 297-306. 

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