Accelerated catalyst aging test

Thus, the accelerated catalyst aging test can be considered to accurately reproduce the tendency of catalyst deterioration in the Z-Former demonstration test. In the case of a sequence consisting of 24 hours per cycle, it is possible to predict catalyst life in 1/4 to 1/8 the time required by the demonstration test assuming reaction/regeneration in... 

The life time of a catalyst is an important criterion for its commercial application. The reforming reactions in most of the cases have been studied only for hours of time on-stream, but not for days or weeks. Superior catalysts need to be evaluated by operating continuously for thousands of hours. Simple accelerated aging test that allows assessment of catalyst life in hours or days rather than the usual priod of months will be helpful. 

In an automobile s catalytic converter, CO and hydrocarbons present in the exhaust gases are oxidized. Unfortunately the effectiveness of these units decreases with use. The phenomenon was studied by Summers and Hegedus in /. Catalysis, 51, 185 (1978) by means of an accelerated aging test on a palladium impregnated porous pellet packed bed converter. From the reported data on hydrocarbon conversion shown below, develop an expression to represent the deactivation rate of this catalyst. 

Accelerated aging tests have been commonly used in facilities ranging from academic bench scale to industrial pilot-plant scale. In such tests, the addition of an accelerant increases the deactivating agent or its precursor, so that a certain Level of deactivation (however measured) is reached at lower run times. In this manner, the performance of a catalyst at a high deactivation level can, in principle, be measured without expending the time and effort required under normal conditions to bring the catalyst to this level of deactivation,... 

Smaller reactor size reduces the cost, improves control, and isolates process variables, however, effects of catalyst aging/deac-tivation as a function of time are not similarly reduced. These effects can be accelerated in the laboratory environment by increased temperature, water partial pressure, contaminant gas partial pressure, and various contaminant metals. As with scaled down equipment, these efforts are not without problems, however, when some catalyst lifetimes are measured in years, this is the only viable solution to meaningful catalyst research and development. This type of testing, coupled with characterization, has resulted in FCC catalysts with less resistance to coking and thus longer service life. 

A typical lifetime of commercial catalysts is 1-10 years. Thus, for a new catalyst product, the final confirmation of the product performance in industry cannot take place until many years after the product has been produced even if accelerated ageing tests have been carried out. 

Equation 12.2 reflects a base case of 9 mg/mile with a 0.29 m2 surface area, ratio of airflow to vehicle speed at 40%, and conversion of base case to 80% from the UAM. The deactivation factor (DF) is DF = (aged ozone conversion/ fresh ozone conversion). To determine the deactivation factor, on-road aging of radiators coated with catalyst was run for 150,000 miles and DFs at that point were determined. Freshly coated radiators were exposed to an accelerated aging test and DFs were calculated and compared for accuracy. Figure 12.4 shows the calculation of deactivation factors for two different radiators with different core geometries. 

Fig. 10.20 Disk currents at 1,600 ipm and 5 mV/s from cyclic voltammetry experiments in O2-saturated 0.5 M H2SO4 solution of an acid leached nitrogen-doped xerogel (N-CX) made from a mixture of resorcinol formaldehyde and cobalt nitrate. The material was pyrolyzed at 800 °C in NH3. The disk current for the same catalyst is also shown after accelerating aging tests (AAT). Tonset for N-CX before AAT is 0.77 V vs. RHE. It is 0.75 V vs. RHE after AAT (according to Fig. 7a in ref. [115] reproduced with permission of The Royal Society of Chemistry)...

The accelerated aging test is adopted for most of the solid catalyst used in heterogeneous catal3dic reaction. For example, the test conditions of heat-resistant stability for China s AllO series, A2 series and A3 series iron catalyst are at 5 MPa, 30,000h and 500°C hold for 20h, the loss of the ammonia concentration of the reactor outlet is not higher than 0.5%, while literature was to evaluate the stability by the reducing degree of activity at 600°C hold for 16 h. 

We took advantage of the dispersibility of Pd Ce02 core-shell structures to deposit them into the porous scaffold of SOFC materials as anode catalysts in order to enhance the thermal stability of these materials. The porous scaffolds were composed of yttrium-stabilized zirconia (YSZ) covered with a film of the conductive oxide lanthanum strontium chromium manganite (LSCM). For comparison of the activity and thermal stability, we prepared other electrodes that were identical except that the catalyst was simply Pd (from Pd(II) nitrate) in one case and a mixture of Pd and CeOg (from Pd(II) and Ce(III) nitrate salts) in the other. All the samples were first calcined at 700 °G to remove any by-products and to stabilize the materials. Then, accelerated aging tests were performed by calcining the samples at 900 °C for 2 hours. Initially we tested all the formulations in symmetric cells, e.g. cells where the anode and cathode materials are the same. The corresponding Nyquist plots are shown in Fig. 7.12(a). 

Marafl et al. (2007,2008) from Kuwait has been working very hard on studies to determine the maximum metal capacity of different catalysts used in hydrodesulfurization of atmospheric residue by accelerated aging tests. 

Marafi, A., Aknarri, M., Stanislaus, A. 2008. The usage of high metal feedstock for the determination of metal capacity of ARDS catalyst system by accelerated aging tests. 

Laboratory steam deactivations represent a significant compromise in the effort to simulate equilibrium catalyst. Since hydrothermal deactivation of FCC catalysts is not rapid in commercial practice, deactivation of the fresh catalyst in the laboratory requires accelerated techniques. The associated temperatures and steam partial pressures are often in substantial excess of those encountered in commercial units. In some instances, the effect of contaminant metals is measured by an independent test not affiliated with steam deactivation. In subsequent yields testing, interactions between different modes of deactivation may be overlooked. Finally, single mode deactivation procedures can not reproduce the complex profile of ages and levels of deactivation present in equilibrium catalyst. 

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