Catalysts activity data

Figure 6.4. Effect of gold loading on ceria upon Au/Ce02 catalyst activity. Data were obtained at 12,000h 1 space velocity, atmospheric pressure Au loading (1) 1 wt% (2) 3 wt% (3) 5 wt%. Reproduced from Andreeva et al.50...

In the following sections, the performance of the imine complexes is discussed. It must be noted [Ila] that comparing catalyst activity data from different studies is only approximate due to their dependence on experimental conditions, that is reactor geometry, stirring procedure, polymerization time, pressure and the like. Therefore it is advantageous to include known complexes for a direct comparison ( benchmarking ) under identical experimental polymerization conditions. It follows that the catalytic activity and productivity obtained for these known catalysts may differ from the ones reported in the literature they are characteristic of the equipment and screening procedure used. 

The authors acknowledge the valuable assistance of Virginia Doud and Nancy Foster of Coming s Technology Division in the preparation of this paper. They are also grateful to Mark Sickels of Arvin Automotive, Phil Weber of Southwest Research Institute, and Paul Stroom of 3M Company for providing durability, back pressure and catalyst activity data. 

Experimental equipment that is useful for the rapid screening of catalysts in support of the global polyethylene business must meet two critical requirements (1) The polymerization reactor needs to be properly designed so that an experiment can be carried out imder steady-state polymerization conditions for a minimum of about 20 minutes in order to provide important catalyst activity data and sufficient polymer for complete characterization. (2) A process model is needed in order to quantitatively determine important kinetic parameters of an experimental catalyst. 

The hterature consists of patents, books, journals, and trade Hterature. The examples in patents may be especially valuable. The primary Hterature provides much catalyst performance data, but there is a lack of quantitative results characterizing the performance of industrial catalysts under industrially reaHstic conditions. Characterizations of industrial catalysts are often restricted to physical characterizations and perhaps activity measurements with pure component feeds, but it is extremely rare to find data characterizing long-term catalyst performance with impure, multicomponent industrial feedstocks. Catalyst regeneration procedures are scarcely reported. Those who have proprietary technology are normally reluctant to make it known. Readers should be critical in assessing published work that claims a relevance to technology. 

The surface area correlates fairly well with the fresh catalyst activity. Upon request, catalyst suppliers can also report the zeolite surface area. This data is useful in that it is proportional to the zeolite content of the catalyst. 

For example, a catalyst with a MAT number of 70 vol% and a 3.0 wt% coke yield will have a dynamic activity of 0.78. However, another catalyst with a MAT conversion of 68 vol% and 2.5 wt% coke yield will have a dynamic activity of 0.85. This could indicate that in a commercial unit the 68 MAT catalyst could outperform the 70 MAT catalyst, due to its higher dynamic activity. Some catalyst vendors ha% c begun reporting dynamic activity data as part of their E-cat inspection reports. The reported dynamic activity data can vary significantly from one test to another, mainly due to the differences in feedstock quality between MAT and actual commercial application. In addition, the coke yield, as calculated by the MAT procedure, is not very accurate and small changes in this calculation can affect the dynamic activity appreciably. 

This paper surveys the field of methanation from fundamentals through commercial application. Thermodynamic data are used to predict the effects of temperature, pressure, number of equilibrium reaction stages, and feed composition on methane yield. Mechanisms and proposed kinetic equations are reviewed. These equations cannot prove any one mechanism however, they give insight on relative catalyst activity and rate-controlling steps. Derivation of kinetic equations from the temperature profile in an adiabatic flow system is illustrated. Various catalysts and their preparation are discussed. Nickel seems best nickel catalysts apparently have active sites with AF 3 kcal which accounts for observed poisoning by sulfur and steam. Carbon laydown is thermodynamically possible in a methanator, but it can be avoided kinetically by proper catalyst selection. Proposed commercial methanation systems are reviewed. 

In other instances, reaction kinetic data provide an insight into the rate-controlling steps but not the reaction mechanism see, for example, Hougen and Watson s analysis of the kinetics of the hydrogenation of mixed isooctenes (16). Analysis of kinetic data can, however, yield a convenient analytical insight into the relative catalyst activities, and the effects of such factors as catalyst age, temperature, and feed-gas impurities on the catalyst. 

The activities of two catalysts, C150-1-01 and another commercial catalyst, were compared (Table XVIII). Catalyst activity was determined (a) from the literature data using their kinetics, and (b) by Equation 5. Then the same procedure was followed for the C150-1-01 catalyst using typical data. The activity ratios are presented in Table XVIII. 

In addition to actual synthesis tests, fresh and used catalysts were investigated extensively in order to determine the effect of steam on catalyst activity and catalyst stability. This was done by measurement of surface areas. Whereas the Brunauer-Emmett-Teller (BET) area (4) is a measure of the total surface area, the volume of chemisorbed hydrogen is a measure only of the exposed metallic nickel area and therefore should be a truer measure of the catalytically active area. The H2 chemisorption measurement data are summarized in Table III. For fresh reduced catalyst, activity was equivalent to 11.2 ml/g. When this reduced catalyst was treated with a mixture of hydrogen and steam, it lost 27% of its activity. This activity loss is definitely caused by steam since a... 

If the catalyst active centers are nonuniform, a time variation of the average value of Kp may be caused by the change of the proportion between the centers with various reactivity during polymerization. However, in the case of chromium oxide catalysts the experimental data show that the... 

Table II represents the data on the reactivity of the propagation centers and their number corresponding to the maximum catalytic activity observed for three typical one-component catalysts. These data were ob-...

The performance of various solvents can be explained with the help of the role of these solvents in the reaction. These solvents help in keeping teth benzene and hydrogen peroxide in one phase. This helps in the easy transport of both the reactants to the active sites of the catalyst. The acetonitrile, and acetone adsorption data on these catalysts (Fig. 6), suggests that acetonitrile has a greater affinity to the catalytic surface than acetone. There by acetonitrile is more effective in transporting the reactants to the catalyst active sites. At the same time, they also help the products in desorbing and vacating the active sites. 

Prior to inclusion of PVP-protected Pt nanoparticles the SBA-15 silica is calcined at 823K for 12h to remove residual templating polymer. Removal of PVP is required for catalyst activation. Due to the decomposition profile of PVP (Figure 6), temperatures > 623 K were chosen for ex situ calcination of Pt/SBA-15 catalysts. Ex-situ refers to calcination of 300-500 mg of catalyst in a tube furnace in pure oxygen for 12-24 h at temperatures ranging from 623 to 723 K (particle size dependent) [13]. Catalysts were activated in He for 1 h and reduced at 673 K in H2 for 1 h. After removal, the particle size was determined by chemisorption. Table 2 is a summary of chemisorption data for Cl catalysts as well as nanoparticle encapsulation (NE) catalysts (see description of these samples in proceeding section). 

When we activated the catalyst system on a large scale, we were unsure of whether the reaction would proceed. The only data for the catalyst activation available to us was in situ IR (React-IR) as shown in Figure 2.3. During activation of the catalyst, a single vibration frequency (-1980 cm"1) of carbon monoxides in Mo(CO)(s became five different frequencies of carbon monoxide in the catalyst solution. This IR data provided us some relief from the risk of running the large scale reaction but did not provide any clues on the structure of the true catalyst. 

Addition of ammonium hydroxide and water were explored to evaluate their influence upon catalyst activity and selectivity. The data in this study suggest that there was little influence of ammonium hydroxide on reaction rate and selectivity. The data, however, were not sufficient to definitively define the role of these additives and investigation of these effects will be the subject of future exploration. Examination of Figure 3 may lead to the conclusion that water is actually harmful to the life of the catalyst but such a preliminary hypothesis is overly simplistic, acknowledging that the ammonium hydroxide additive comprises 70% water. 

The activity data obtained on SnPt and ReSnPt catalysts are given in Table 3. The comparison of the data given in the first row of Table 2 and Table 3... 

There are several factors that may be invoked to explain the discrepancy between predicted and measured results, but the discrepancy highlights the necessity for good pilot plant scale data to properly design these types of reactors. Obviously, the reaction does not involve simple first-order kinetics or equimolal counterdiffusion. The fact that the catalyst activity varies significantly with time on-stream and some carbon deposition is observed indicates that perhaps the coke residues within the catalyst may have effects like those to be discussed in Section 12.3.3. Consult the original article for further discussion of the nonisothermal catalyst pellet problem. 

The first-stage effluent temperature has been limited to 560 °C in order to prevent excessive catalyst activity losses. The heat of reaction data is slightly inconsistent with the reported activation energies, but use of this expression demonstrates the ease with which temperature dependent properties may be incorporated in the one-dimensional model. 

Figure 9. Catalyst activity of lanthanides in diene polymerization. Data from Ref. 22.

Table VI. Effect of R m VO(OR)2Cl on catalyst activity. Polymerization conditions moiar ratio butadiene, propylene is 1.1, monomer concentration, 31 wt. % in -hexane reaction, — 50°C catalyst, 0.8 mmol VO(OR)2Cl phm, 6.0 mmol i-Bu3Al phm reaction time, 3 h. Data from Ref. 19.

Results of EXAFS Fitting3 of H2-activated Catalysts for Data Acquired Near the Co K Edge... 

In this work, a detailed kinetic model for the Fischer-Tropsch synthesis (FTS) has been developed. Based on the analysis of the literature data concerning the FT reaction mechanism and on the results we obtained from chemical enrichment experiments, we have first defined a detailed FT mechanism for a cobalt-based catalyst, explaining the synthesis of each product through the evolution of adsorbed reaction intermediates. Moreover, appropriate rate laws have been attributed to each reaction step and the resulting kinetic scheme fitted to a comprehensive set of FT data describing the effect of process conditions on catalyst activity and selectivity in the range of process conditions typical of industrial operations. 

---