Catalysts measurement

The reducibility of the catalyst is demonstrated in Figure 6 which shows the activity of catalysts, measured as described above, after reduction to constant activity at temperatures of 280°-350°C (536°-662°F). It will be seen that ICI catalyst 11-3 compares favorably with other catalysts which contain larger amounts of alumina and consequently are more difficult to reduce at acceptable temperatures. 

Table 1 shows chemical compositions of clay catalysts measured by XRF analysis. Si02 and AI2O3 are main components of the three clay catalysts with minor amount of Na20, Fc203 and others. The Si/Al ratio increased from HH [Pg.434]

Fig. 4 shows the current density over the supported catalysts measured in 1 M methanol containing 0.5 M sulfuric acid. During forward sweep, the methanol electro-oxidation started to occur at 0.35 V for all catalysts, which is typical feature for monometallic Pt catalyst in methanol electro-oxidation [8]. The maximum current density was decreased in the order of Pt/CMK-1 > Pt/CMK-3 > Pt/Vulcan. It should be noted that the trend of maximum current density was identical to that of metal dispersion (Fig. 2 and Fig. 3). Therefore, it is concluded that the metal dispersion is a critical factor determining the catalytic performance in the methanol electro-oxidation.

A full analysis of the rate expression reveals that all data on the Cu(lOO) single crystal are modeled very well, as shown in Fig. 8.10. Even more important is that the model also describes data obtained on a real catalyst measured under considerably different conditions reasonably well, indicating that the micro-kinetic model captures the most important features of the methanol synthesis (Fig. 8.11). 

Perrichon, V., Retailleau, L., Bazin, P. et al. (2004) Metal dispersion of Ce02—Zr02 supported platinum catalysts measured by H2 or CO chemisorption, Appl. Catal. A, 260, 1. 

XRD powder patterns of fresh and used catalysts, measured at room temperature on a Bruker D8 Advance diffractometer equipped with Sol-X detector, were subjected to Rietveld structure refinement in Immm space group using the GSAS package (Larson and Von Dreele, 1994). 

Catalyst characterization by the relative value of slopes, a , is most useful when parallel trends in the properties of the catalysts, measured by other probes, chemical or physical, are discovered. Examples are the estimation of acid strength of the surface sites or the estimation of energy of interaction between surface atoms on the basis of shifts in spectra. All of the quantities used for comparison must be intensive, that is, they must express some form of energy or be proportional to energy. 

Stable catalytic activity was observed with praseodymium chloride pretreated under an oxygen stream at 750°C for 15 h (Figure 4). The longer pretreatment produced high selectivity to C2+ compounds, that is, 58.8% in the presence of TCM and 58.5% in the absence of TCM after 0.5 h on-stream while methane conversions were 19.7 and 18.6%, respectively. Without TCM the conversion and the selectivity decreased gradually to 17.0 and 54.0% after 6 h on-stream, respectively. The catalytic activity was partially restored by addition of TCM to the reaction stream for 1 h. The conversion was 17.3% and the selectivity was 55.0% after 0.5 h on-stream following the period of the TCM feeding. The BET surface areas of the catalysts measured after the reactions in the presence and absence of TCM were both 1.5 m g The XRD patterns of the catalysts used for the reactions were identical with that of praseodymium oxychloride. A small amount of methyl chloride was detected when praseodymium chloride was used as a precursor of the catalyst both in the presence and in the absence of TCM. 

The input parameters for a microkinetic model may be taken from measured adsorption and reaction rates for the catalyst, measured heats of adsorption together with thermodynamic data for the gas (or liquid-) phase above the catalyst. 

Weisz and Prater derived a criterion of strong resistance effects inside catalyst particles depending only on the concentration of the feed, catalyst measurables, and the observed rate (—robs) for a first-order reaction ... 

Where the rate of reaction depends upon the presence of an accidental catalyst, measurements are characterized by great lack of reproducibility. Many homogeneous reactions, on the other hand, have quite definite and reproducible rates. For example, the measurements of Bodenstein and of Kistiakowsky on the rate of decomposition of hydrogen iodide agree excellently, as do those of numerous investigators of the rate of decomposition of nitrogen pentoxide. 

The catalyst contained 10% platinum deposited on activated carbon. This high platinum content (20 times more than in the commercial catalyst) made the activity of the catalyst more stable, thus facilitating the studies of kinetics. The surface of platinum in 1 g of the catalyst measured by hydrogen chemisorption was 2 m2. Since the concentrations of H2 and NO in the... 

Table 28.1 Carbon content (wt%) of the catalyst measured by the CHN analyzer after activation and reaction...

Characterization of the Surfaces of Catalysts Measurements of the Density of Surface Faces for High Surface Area Supports. - It has always been a tenet of theories of catalysis that certain reactions will proceed at different rates on different surface planes of the same crystal. Experiments with metal single crystals have vindicated this view by showing that the rate of hydrogenolysis of ethane on a nickel surface will vary from one plane to another. In contrast the rate of methanation remains constant for the same planes.4 Because of this structure sensitivity of catalytic processes there is a requirement for methods of determining the number of each of the different planes which a catalyst and its support may expose at their surfaces. Electron microscopy studies of 5nm Pt particles supported upon graphite show them to be cubo-octahedra with surfaces bound by (111) and (100) planes.5 Similar studies of Pd and Pt prepared by evaporation reveal square pyramids of size 60-200 A bounded by incomplete (111) faces.6... 

Characterization of the Bulk Properties of Catalysts Measurements of Particle-size Distribution Functions of Supported Catalysts -... 

Fig. 1. Quick EXAFS spectra of the sulfidation of a M0/AI2O3 catalyst, measured during continuous heating of the catalyst in 5% H2S in H2 from room temperature to 673 K at 5 K/min and holding at 673 K for 30 min.

Fig. 8.26. I nitial rates for different zeolite BEA-based catalysts, measured in open round-bottomed glass flask reactors (160 mg catalyst, 160 °C, atmospheric pressure).

This unique micro structure can be described as an intermediate stage between a supported catalyst and a bulk metallic sponge or skeletal Raney-type catalyst. It enables a reasonably high dispersion of Cu and exposure of many Cu-ZnO interfaces at a high total Cu content. The specific Cu surface area (SACu) of methanol catalysts can be determined by reactive N20 titration [59, 60], which causes surface oxidation of the Cu particles and allows calculation of SAcu from the amount of evolved N2. The SACu of state-of-the-art methanol synthesis catalysts measured by this method... 

Figure 1. FTIR spectrum of the 5 wt-% Pt/Al203 catalyst measured after prereduction at 673 K (catalyst cleaning) and cooling to 313 K atmosphere 3 bar C02 +12 bar H2.

The catalyst deactivation model developed in this paper accounts for the nonsteady-state activity of commercial catalysts measured using accelerated sulfur aging experi-... 

In a number of works, C has been correlated with the physical surface of the catalyst measured before the polymerization. This correlation, however, may be misleading because the catalyst can disintegrate during the catalyst/organometal interaction and particularly during the polymerization. Thus, new surface can be exposed leading to a formation of additional active centers. Discussion of these questions is out of the scope of the present paper. 

At our knowledge, this is the first time that the catalytic behavior of Cu-Al-MCM-41 for the HC-SCR of NO is reported. HC-SCR of NO was previously reported on the Pt-MCM-41, Rh-MCM-41 and Co-MCM-41 catalysts [8]. Pt-MCM-41 resulted the most active catalyst, but no comparison was made with the activity of Pt-ZSM-5 catalysts measured under the same experimental conditions. 

Dispersions of Four Catalysts. Measured by Four Different Methods Chemisorption. 

Walendziewski (75) observed that the total acidity per unit surface area of CoMoP/Al catalysts measured by NH3 TPD increases with increasing phosphorus loading (Fig. 25). Chadwick et al. (60) reported that the surface acidity of NiMoP/Al catalysts measured by pyridine adsorption increased slightly as a result of phosphorus addition. 

Lopez-Agudo et al. (69) reported that the sulfidation of nickel in NiP/Al catalysts, measured by XPS, is not influenced by phosphorus addition. On the other hand, Iwamoto and Grimblot (67) found that phosphorus increases sulfidation of nickel in NiP/Al at 400°C because phosphorus prevents the formation of stable nickel aluminate species. A similar explanation was also proposed for nickel reduction 102). 

Figure 10.15. Plot of O-aloms consumed in the first CO pulse ( -molcs 0/g-cal) as a function of the theoretical bulk oxygen capacity of the catalyst (as PdO). The solid curve connects data for catalysts that contain no oxygen storage material. Also shown at right is the surface oxygen capacity for each catalyst measured by a CO methanation technique. [32]...

Main physical properties of the catalysts, measured in this work, are shown in Table... 

Katsanos, N.A. Gavril, D. Kapolos, J. Karaiskakis, G. Surface energy of solid catalysts measured by inverse gas chromatography. J. Colloid Interface Sci. 2003, 270 (2), 455-461. 

Note that the farther away the electric potential of the carbon surface is from the potential of zero charge point ( pzc) l e higher the disjoining pressure is. In principle, this may result in a systematic variation of the support pore size in Me/C catalysts with potential (similar to the electrocapillary curve [96,97]) and consequently the efficiency of metal particle blocking by the pore walls. Such behavior of porous carbons obviously can influence the measurements of the electrochemically active surface area and might be one of the reasons for the observed correlation between the apparent dispersion of Pt/C catalysts, measured by cyclic voltammetry, and pHpzc of the supports [95], whereas no noticeable difference in the particle size has been observed with HRTEM. Undoubtedly, this problem needs further investigation. 

To see if the time dependence of the chemisorption was caused by a slow establishment of H2 chemisorption at the Rh metal surface, the measurements were also carried out for a 3.7 wtX Rh/SiOj catalyst (silica Grace S.P. 2-324.382, pore volume 1.2 ml g- and surface area 290 m g-1) after reduction at 500 C. The H2 chemisorption of this catalyst measured after a day under H2 differed only 10% from that measured directly after reduction, evacuation and cooling (H/Rh= 0.46 and 0.42, respectively). Thus slowness of H2 chemisorption onto the metal cannot be the reason for the time dependence of the H2 chemisorption on the Rh/R-Ti02 catalyst. 

The specificity of the catalyst, measured by the ratio of CO2 to CO, was imaflfected by the prior neutron irradiation but was altered by the y-irradiation. The specific activity for dehydrogenation appeared in fact to go through a maximum with increasing y dose, the ratio CO2/CO being smaller both below and above 6 x lO ev/gm. Somewhat surprisingly, in view of the results described below 188), the surface areas of the oxides prepared from irradiated hydroxides were smaller in every case (125-140 m /gm) than those from nonirradiated ones (173 m /gm). 

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