Volumetric catalytic activity

The Fe203-Cr203 catalysts are characterized by a lifetime of 3—5 years, depending mainly on the operation temperature. They can tolerate sulfur up to 1000 ppm. Their major drawbacks are the toxicity of the water-soluble Cr and the low volumetric catalytic activity (GHSV = 10.000—15.000/h), especially at low temperatures when CO conversion is favored thermodynamically, needing the utilization of large catalyst bed volumes. 

Symbols AD, adsorption CO, catalytic activity for reactions other than desulfurization CS, catalytic activity for desulfurization EC, ESCA ES, ESR G, gravimetric IR, infrared MS, magnetic susceptibility OO, other PP, physical properties RS, reflectance spectra V, volumetric XR, X-ray diffraction. 

The problem with sulfide catalysts (hydrotreatment) is to determine the active centres, which represent only part of their total surface area. Chemisorption of O2, CO and NO is used, and some attempts concern NIL, pyridine and thiophene. Static volumetric methods or dynamic methods (pulse or frontal mode) may be used, but the techniques do not seem yet reliable, due to the possible modification (oxidation) of the surface or subsurface regions by O2 or NO probe molecules or the kinetics of adsorption. CO might be more promising. Infrared spectroscopy, especially FTIR seems necessary to characterise co-ordinativcly unsaturated sites, which are essential for catalytic activity. CO and NO can also be used to identify the chemical nature of sites (sulfided, partially reduced or reduced sites). For such... 

The chemical transformation of Ru-complexes in faujasite-type zeolites in the presence of water and of carbon monoxide-water mixtures is reviewed and further investigated by IR, UV-VIS spectroscopic and volumetric techniques. The catalytic activity of these materials in the watergasshift reaction was followed in a parallel way. The major observations could be rationalized in terms of a catalytic cycle involving Ru(I)bis and triscarbonyl intermediates stabilized in the supercages of the faujasite-type zeolite. The turnover frequency of this cycle is found to be determined by the nature, number and position of the charge compensating cations, as well as by the nature of the ligands present in the Ru-coordination sphere. 

For the TBR, spherical catalyst particles of uniform size with the catalytically active material either uniformly distributed throughout the catalyst or present in a shell were considered. For the MR, channels of square cross section were assumed to have walls covered by the washcoat distributed in such a way that the comers are approximated by the circle-in-square geometry, while the sides are approximated by a planar slab geometry. The volumetric load of catalytic material was a function of the washcoat thickness... 

The effects of SCFs on the catalytic activity of methanol synthesis are shown in Table 3. It is obvious that the gas phase (He) exhibited the lowest total carbon conversion (about 16.4%). As methanol synthesis is a highly exothermic reaction, the low conversion in gas phase possibly resulted from the heat of reaction which cannot be removed rapidly from the catalyst bed. The total carbon conversion increased to 45.6% when SC-Ce was introduced into the reaction. This illustrates that the SCF enhanced the reaction activity of methanol synthesis. The rate of reaction was possibly enhanced while the experiment was operated in the mixture critical region because of a favorable pressure dependence of the reaction rate constant as well as the imusual volumetric behavior of heavy solutes solubilized in an SCF solvent [16]. 

In total 12 experiments were carried out. Three volumetric feed flows were used (1.3, 3.3 and 5.3 ml/s) with two reactor volumes (10 ml and 6.5 ml). Each experiment was realized without and with an ultrasonic field of 40 Watt/cm. The precipitate was filtrated at room temperature and washed several times with deionizated water. The filtrate was dried for 12 h in a furnace at 65 °C. As a test for the catalytic activity of the Mn02 particles evolution of O2 from H2O2 was used. For these tests a sieve fraction between 63 pm and 80 pm of dried Mn02 was used. An amount of 0.05 g of manganese dioxide was given into a beaker with a solution of hydrochloric acid and hydrogen peroxide in water. The solid acts as a catalyst for the formation of oxygen (4a) and dissolutes simultaneously in the reaction (4b). 

For some catalysts, it was found that besides the contents of iron and nitrogen, the catalytic activity was dependent on the micropore content of the final catalyst [36, 37]. In order to illustrate the importance of the micropores, these catalysts are labeled as p-Fe-N-C in this essay. So far, these are the Me-N-C catalysts that reach the highest volumetric current densities [10] which are basically determined by their very high turnover frequency [31] (see the text on TOF, below). 

As FBMRs circumvent the external mass transfer limitations that adversely affect the performance of PBMRs to a large extent, the volumetric production capacity in FBMRs is limited by the relatively low permeation rate through the membranes (provided that the catalytic activity is sufEciently high). 

Catalytic kinetic resolution can be the method of choice for the preparation of enantioenriched materials, particularly when the racemate is inexpensive and readily available and direct asymmetric routes to the optically active compounds are lacking. However, several other criteria-induding catalyst selectivity, efficiency, and cost, stoichiometric reagent cost, waste generation, volumetric throughput, ease of product isolation, scalability, and the existence of viable alternatives from the chiral pool (or classical resolution)-must be taken into consideration as well... 

The present paper focuses on the interactions between iron and titania for samples prepared via the thermal decomposition of iron pentacarbonyl. (The results of ammonia synthesis studies over these samples have been reported elsewhere (4).) Since it has been reported that standard impregnation techniques cannot be used to prepare highly dispersed iron on titania (4), the use of iron carbonyl decomposition provides a potentially important catalyst preparation route. Studies of the decomposition process as a function of temperature are pertinent to the genesis of such Fe/Ti02 catalysts. For example, these studies are necessary to determine the state and dispersion of iron after the various activation or pretreatment steps. Moreover, such studies are required to understand the catalytic and adsorptive properties of these materials after partial decomposition, complete decarbonylation or hydrogen reduction. In short, Mossbauer spectroscopy was used in this study to monitor the state of iron in catalysts prepared by the decomposition of iron carbonyl. Complementary information about the amount of carbon monoxide associated with iron was provided by volumetric measurements. 

The batch reactor is characterized by its volume, Fr, and the holding time, t, that the fluid has spent in the reactor. Flow reactors are usually characterized by reactor volume and space time, r, with the latter defined as the reactor volume divided by the volumetric flow rate of feed to the reactor. The physical significance of r is the time required to process a volume of fluid corresponding to Rr. For catalytic reactions, the space time may be replace by the site time, xp, defined as the number of catalytic sites in the reactor, Sr, divided by the molecular flow rate of feed to the reactor, F. The physical interpretation of rp is the time required to process many molecules equal to the number of active sites in the reactor. 

It is rather atypical that a photochemical reaction will proceed in a single molecular pathway. Thus, several elementary steps are involved. Normally, the majority of them are dark (thermal) reactions while, ordinarily, one activation step is produced by radiation absorption by a reactant molecule or a catalyst. From the kinetics point of view, dark reactions do not require a different methodological approach than conventional thermal or thermal-catalytic reactions. Conversely, the activation step constitutes the main distinctive aspect between thermal and radiation activated reactions. The rate of the radiation activated step is proportional to the absorbed, useful energy through a property that has been defined as the local volumetric rate of photon absorption, LVRPA (Cassano et ak, 1995 Irazoqui et al., 1976) or the local superficial rate of photon absorption, LSRPA (Imoberdorf et al., 2005). The LVRPA represents the amount of photons that are absorbed per unit time and unit reaction volume and the LSRPA the amount of photons that are absorbed per unit time and unit reaction surface. The LVRPA is a property that must be used when radiation absorption strictly occurs in a well-defined three-dimensional (volumetrical) space. On the other hand, to... 

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