Catalyst physical

Important physical properties of catalysts include the particle size and shape, surface area, pore volume, pore size distribution, and strength to resist cmshing and abrasion. Measurements of catalyst physical properties (43) are routine and often automated. Pores with diameters <2.0 nm are called micropores those with diameters between 2.0 and 5.0 nm are called mesopores and those with diameters >5.0 nm are called macropores. Pore volumes and pore size distributions are measured by mercury penetration and by N2 adsorption. Mercury is forced into the pores under pressure entry into a pore is opposed by surface tension. For example, a pressure of about 71 MPa (700 atm) is required to fill a pore with a diameter of 10 nm. The amount of uptake as a function of pressure determines the pore size distribution of the larger pores (44). In complementary experiments, the sizes of the smallest pores (those 1 to 20 nm in diameter) are deterrnined by measurements characterizing desorption of N2 from the catalyst. The basis for the measurement is the capillary condensation that occurs in small pores at pressures less than the vapor pressure of the adsorbed nitrogen. The smaller the diameter of the pore, the greater the lowering of the vapor pressure of the Hquid in it. 

The ash content of the DO is affected by the reactor cyclone s performance and catalyst physical properties. To meet the CBFS ash requirement (maximum of 0.05 wt%), DO product may need to be filtered for the removal of the catalyst fines. 

Once the unit is running well, it is often assumed that the aeration system is sized properly, but changes in the catalyst physical properties and/or catalyst circulation rate may require a different purge rate. It should be noted that aeration rate is directly proportional to catalyst circulation rate. Trends of the E-cat properties can indicate changes in the particle size distribution, which may require changes in the aeration rate. Restriction orifices could be oversized, undersized, or plugged with catalyst, resulting in over-aeration, under-aeration, or no aeration. All these phenomena cause low pressure buildup and low slide valve differential. 

Consider reformulating the catalyst—custom formulations are available. Increasing rare-earth content can reduce the wet gas rate. Catalyst is usually selected for properties other than its ability to flow. However, if it does not flow, it is not going to work well. Catalyst physical properties should be compared with those of catalysts that have circulated well. Evaluate the economics of using metal passivation additives and other catalyst enhancing additives. 

Model formulation. After the objective of modelling has been defined, a preliminary model is derived. At first, independent variables influencing the process performance (temperature, pressure, catalyst physical properties and activity, concentrations, impurities, type of solvent, etc.) must be identified based on the chemists knowledge about reactions involved and theories concerning organic and physical chemistry, mainly kinetics. Dependent variables (yields, selectivities, product properties) are defined. Although statistical models might be better from a physical point of view, in practice, deterministic models describe the vast majority of chemical processes sufficiently well. In principle model equations are derived based on the conservation law ... 

Improved Filtration Rate Filterability is an important powder catalyst physical property. Sometimes, it can become more important than the catalyst activity depending on the chemical process. When a simple reaction requires less reaction time, a slow filtration operation can slow down the whole process. From a practical point of view, an ideal catalyst not only should have good activity, but also it should have good filtration. From catalyst development point of view, one should consider the relationship between catalyst particle size and its distribution with its catalytic activity and filterability. Smaller catalyst particle size will have better activity but will generally result in slower filtration rate. A narrower particle size distribution with proper particle size will provide a better filtration rate and maintain good activity. 

Several sol-gel entrapped catalysts are likely to soon find commercial applications. A variety of transition metal catalysts physically entrapped in silica matrices as ion pairs generated from the metal halides and quaternary ammonium or phosphonium salts developed in the mid-1990s by Avnir and Blum resulted in truly heterogeneous, stable and... 

Spengler, ]. Anderle, F. Bosch, E. Grasselli, R. K. Pillep, B. Behrens, R Lapina, O. B. Shubin, A. A. Eberle, H. ]. Knozinger, H. Antimony Oxide-Modified Vanadia-Based Catalysts—Physical Characterization and Catalytic Properties. J. Phys. Chem. B 2001, 105, 10772-10783. 

Optimizing the fresh catalyst physical properties including particle density, PSD, and attrition resistance is critical to maintaining acceptable fluidization and resulting circulation of the catalyst inventory. Excessive attrition of the catalyst will lead to nonuniform fluidization and disrupt circulation. Potential sources of attrition include ... 

The circulating catalyst physical properties have a direct impact on fluidization and stable standpipe operation. Mechanical problems may cause a loss of catalyst fines, or a change in catalyst density both of which will impact fluidization and may require adjustment to the standpipe aeration. 

Figure 12 shows the XANES and FT-EXAFS spectra of the titanium oxide catalysts chemically doped with Cr ions (a and A) and physically implanted with Cr ions (b and B). Analyses of these XANES and FT-EXAFS spectra show that in the titanium oxide catalysts chemically doped with Cr ions by an impregnation or sol-gel method, the ions are present as aggregated Cr oxides having an octahedral coordination similar to CriOs and tetrahedral coordination similar to CrOs, respectively. On the other hand, in the catalysts physically implanted with Cr ions, the ions are present in a highly dispersed and isolated state in octahedral... 

To remind ourselves that the proper objects of all catalyst research are more powerful and selective syntheses, we have R. F. Heck s chapter describing a wide range of new organic halide reaction catalyses by metal carbonyls and related catalysts. Physics may be fun but chemistry is our bread and butter, and homogeneous catalysis is an area in which we must expect to give increasing space in our Advances in Catalysis in the future. 

Recently, we reported detailed descriptions of hydrocarbon chain growth on supported Ru catalysts (7,8) we showed that product distributions do not follow simple polymerization kinetics and proposed a diffusion-enhanced olefin readsorption model in order to account for such deviations (7,8). In this paper, we describe this model and show that it also applies to Co and Fe catalysts. Finally, we use this model to discuss a few examples from the literature where catalyst physical structure and reaction conditions markedly influence hydrocarbon product distributions. 

Mul, G., Banares, M.A., Gortez, G. Garda, van der Linden, B., Khatib, S.J. and Moulijn, J.A. (2003) MultiTRACK and operando Raman-GC study of oxidative dehydrogenation of propane over alumina-supported vanadium oxide catalysts. Physical Chemistry Chemical Physics, 5 (20), 4378-83. 

Type Silicone emulsion silicone polymer system Products DOW CORNING 1111 Emulsion now CORNING T4-0149 crosslinker DOW CORNING 1R2A or 164 catalyst Physical Form Water dilutable liquids... 

Catalysts regenerated by methods (A) and (B) are evaluated on the basis of bench-scale activity tests, characterization of catalyst physical and chemical properties, and physical integrity tests, such as particle attrition resistance,... 

Wei, J. and Iglesia, E. Isotopic and kinetic assessment of the mechanism of methane reforming and decomposition reactions on supported iridium catalysts. Physical Chemistry Chemical Physics, 2004, 6, 3754. 

Velu, S., Suzuki, K., Gopinath, C.S., Yoshida, H., and Hattori, T. XPS, XANES and EXAFS investigations of Cu0/Zn0/Al203/Zr02 mixed oxide catalysts. Physical Chemistry Chemical Physics, 2002, 4, 1990. 

The catalyst has been developed by Intevep, S. A. [4,5] and is being commercialized by AZKO NOBEL Chemie from Holland under the trademark INT-R1 High molecular weight compounds are able to be processed with the catalyst due to its special pore distribution. Therefore, it can be used to treat feedstocks with a significant asphaltene content without losing its high desulfurization and demetallization activity. Also, the catalyst has a high metal retention capacity and allows for moderate conversion of the 510°C fraction. INT-R1 catalyst physical properties are shown in Table 1. 

Multimetallic catalysts (physical mixtures of monometallic catalysts) ... 

Thomas, L Tanner, R Gill, P Wells, R Bailie, JE Kelly, G Jackson. SD Hutchings, G. A Idol condensation reactions of acetone over alkali-modified vanadium phosphate catalysts. Physical Chemistry Chemical Physics, 2002 4,4555-4560. 

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