Catalyst powder

Activated Raney nickel is pyrophoric and should never be allowed to become dry. Thus decanting is preferred to filtration, and when decanting, a small amount of solvent must always be left behind to cover the catalyst powder. For safe disposal, the spent catalyst should be slurried in water and flushed down the drain under running water. 

Why are catalyst powders usually pressed into bodies of particular shapes ... 

Catalytic activity tests have been performed in a quartz microreactor (I.D.=0.8 cm) filled with 0.45 g of fine catalyst powders (dp=0 1 micron). The reactor has been fed with lean fiiel/air mixtures (1.3% of CO, 1.3% of H2 and 1% of CH4 in air resp ively) and has been operated at atmospheric pressure and with GHSV= 54000 Ncc/gcath The inlet and outlet gas compositions were determined by on-line Gas Chromatography. A 4 m column (I D. =5mm) filled with Porapak QS was used to separate CH4, CO2 and H2O with He as carrier gas. Two molecular sieves (5 A) columns (I D.=5 mm) 3m length, with He and Ar as carrier gases, were used for the separation and analysis of CO, N2, O2, CH4, and H2, N2, O2 respectively... 

The placement of catalysts/carriers in micro channels can be done by various means. In a conventionally oriented variant, catalyst powders or small grains are inserted as mini fixed beds [7]. However, more specific catalyst arrangements are also known, originally designed for novel ways of processing at the macro scale, such as catalyst filaments [8], wires [9] and membranes (Figure 3.2) [10, 11]. 

Thin-fdm was prepared from a slurry of catalyst powder which was prepared from 10 mg catalyst in 5 ml of 2-propanol. The catalyst slurry was sonicated for 30 min. and allowed to sit stagnant overnight. Before preparing the films, the slurry was sonicated for 15 min., 20 drops (0.1 ml) were added onto a ZnSe trough plate internal reflection element (022-2010-45, Pike Technologies). The solvent was allowed to evaporate, the procedure was repeated a total of five times. After drying in air at room temperature, the catalyst thin-film was ready for 2-propanol dehydrogenation studies. 

The hydrogenation of 3-hydroxy propan al (HPA) to 1,3-propanediol (PD) over Ni/SiOi/AEO, catalyst powder was studied by Professor Hoffman s group at the Friedrich-Alexander University in Erlagen, Germany (Zhu et al., 1997). PD is a potentially attractive monomer for polymers like polypropylene terephthalate. They used a batch stirred autoclave. The experimental data were kindly provided by Professor Hoffman and consist of measurements of the concentration of HPA and PD (Chpa< Cpd) versus time at various operating temperatures and pressures. 

Let us reconsider the hydrogenation of 3-hydroxypropanal (HPA) to 1,3-propanediol (PD) over Ni/Si02/Al203 catalyst powder that used as an example earlier. For the same mathematical model of the system you are asked to regress simultaneously the data provided in Table 16.23 as well as the additional data given here in Table 16.28 for experiments performed at 60°C (333 K) and 80°C (353 K). Obviously an Arrhenius type relationship must be used in this case. Zhu et al. (1997) reported parameters for the above conditions and they are shown in Table 16.28. 

Catalysts - A commercial Raney nickel (RNi-C) and a laboratory Raney nickel (RNi-L) were used in this study. RNi-C was supplied in an aqueous suspension (pH < 10.5, A1 < 7 wt %, particle size 0.012-0.128 mm). Prior to the activity test, RNi-C catalyst (2 g wet, 1.4 g dry, aqueous suspension) was washed three times with ethanol (20 ml) and twice with cyclohexane (CH) (20 mL) in order to remove water from the catalyst. RCN was then exchanged for the cyclohexane and the catalyst sample was introduced into the reactor as a suspension in the substrate. RNi-L catalyst was prepared from a 50 % Ni-50 % A1 alloy (0.045-0.1 mm in size) by treatment with NaOH which dissolved most of the Al. This catalyst was stored in passivated and dried form. Prior to the activity test, the catalyst (0.3 g) was treated in H2 at 250 °C for 2 h and then introduced to the reactor under CH. Raney cobalt (RCo), a commercial product, was treated likewise. Alumina supported Ru, Rh, Pd and Pt catalysts (powder) containing 5 wt. % of metal were purchased from Engelhard in reduced form. Prior to the activity test, catalyst (1.5 g) was treated in H2 at 250 °C for 2 h and then introduced to the reactor under solvent. 10 % Ni and 10 % Co/y-Al203 (200 m2/g) catalysts were prepared by incipient wetness impregnation using nitrate precursors. After drying the samples were calcined and reduced at 500 °C for 2 h and were then introduced to the reactor under CH. 

M/g-catalyst initial concentrations. The first sample for each experiment was taken for time equal to zero minutes and filtered through a 0.45 pm hydrophilic Millipore filter to remove catalyst powder into a capped vial for subsequent analysis. 

The catalyst powders were compressed to thin disks under a pressure of about 50 kg/cm2, with the exception of the alumina-supported catalysts which required a pressure of 1500 kg/cm2 to obtain reasonable transmittance. The samples were reduced in a stream of hydrogen supplied at a rate of 10 1 hr-1 (SV 30,000 hr-1). The temperatures of reduction were 350°-450°C for the nickel samples, 475°C for the palladium samples, and 425°C for the iridium catalysts. 

Catalyst powders with carefully specified particle size distribution have been known to possess good fluidization characteristics. Generally, addition of fine particles to coarse particles tends to improve the latter s fluidization characteristics. Experiments were thus conducted on binary particle mixtures, each consisting of a fairly close particle size distribution. 

K. Lourvanij and G. L. Rorrer, Reaction rates for the partial dehydration of glucose to organic acids in solid-acid, molecular-sieving catalyst powders,... 

FIGURE 9.6 Apparatus for time resolution kinetic in FT-measurements. Quick ampoule sampling, internal references, accurate control of flows and pressure, precise zero time, accurate mixing of flows, and catalyst powder on inert particles. 

The catalyst was prepared by impregnating y-alumina (Alon) to incipient wetness using an aqueous solution of (PtClg). After impregnation, the powder was dried, and calcined in air at 773 K (500°C) for 2 h. The infrared disc was prepared by compressing 0.08 g of the catalyst powder at 58 840 N. The properties of the catalyst disc are listed in Table I. 

UNIPOL [Union Carbide Polymerization] A process for polymerizing ethylene to polyethylene, and propylene to polypropylene. It is a low-pressure, gas-phase, fluidized-bed process, in contrast to the Ziegler-Natta process, which is conducted in the liquid phase. The catalyst powder is continuously added to the bed and the granular product is continuously withdrawn. A co-monomer such as 1-butene is normally used. The polyethylene process was developed by F. J. Karol and his colleagues at Union Carbide Corporation the polypropylene process was developed jointly with the Shell Chemical Company. The development of the ethylene process started in the mid 1960s, the propylene process was first commercialized in 1983. It is currently used under license by 75 producers in 26 countries, in a total of 96 reactors with a combined capacity of over 12 million tonnes/y. It is now available through Univation, the joint licensing subsidiary of Union Carbide and Exxon Chemical. A supported metallocene catalyst is used today. 

The use of EM (except in the special case of SEM) demands that the catalyst, whether mono-or multi-phasic, be thin enough to be electron transparent. But, as we show below, this seemingly severe condition by no means restricts its applicability to the study of metals, alloys, oxides, sulfides, halides, carbons, and a wide variety of other materials. Most catalyst powder preparations and supported metallic catalysts, provided that representative thin regions are selected for characterization, are found to be electron transparent and thus amenable to study by EM without the need for further sample preparation. 

Several conditions must be met for successful ETEM investigations. Thin, electron-transparent samples are necessary—this requirement can usually be met with most catalyst powders. Ultrahigh-purity heater materials and sample grids capable of withstanding elevated temperature and gases are required (such as those made of stainless steel or molybdenum). The complex nature of catalysis with gas environments and elevated temperatures requires a stable design of the ETEM instrument to simulate realistic conditions at atomic resolution. 

Conventional HRTEM operates at ambient temperature in high vacuum and directly images the local structure of a catalyst at the atomic level, in real space. In HRTEM, as-prepared catalyst powders can be used without additional sample preparation. The method does not normally require special treatment of thin catalyst samples. In HRTEM, very thin samples can be treated as WPOs, whereby the image intensity can be correlated with the projected electrostatic potential of the crystal, leading to the atomic structural information characterizing the sample. Furthermore, the detection of electron-stimulated XRE in the EM permits simultaneous determination of the chemical composition of the catalyst. Both the surface and sub-surface regions of catalysts can be investigated. 

In addition to the external forces, the catalyst must also resist internal forces imposed on the pellet as phase transitions in the catalyst material progress. These transitions, including e.g. transformation of the amorohous silica carrier into crystalline a-cristobalite, precipitation of V4+ and compounds, and destruction of the carrier by the melt, may eventually cause the catalyst to break up in smaller particles or even to catalyst powder. 

To facilitate its application in organic synthesis, we developed a lyophilized cell powder of Sphingomonas sp. HXN-200 as a biohydroxylation catalyst. Hydro-xylation of A-benzyl-piperidine with such catalyst powder showed 85% of the activity of a similar hydroxylation with frozen/thawed cells, shown in Figure 15.6. The fact that rehydrated lyophilized cells are able to carry out such a reduced nicotinamide adenine dinucleotide (NADH)-dependent hydroxylation indicates that these cells are capable of retaining and regenerating NADH at rates equal to or exceeding the rate of hydroxylation. To our knowledge, this is the first example of the use of lyophilized cells for a cofactor-dependent hydroxylation. 

Kiwi, J., Morrison, C. 1984. Heterogeneous photocatalysis-dynamics of charge-transfer in lithium-doped anatase-based catalyst powders with enhanced water photocleavage under ultraviolet-irradiation. J Phys Chem 88 6146-6152. 

Neto and co-workers examined the ex situ Pt L3 EXAFS for a series of PtRu catalyst powders in air of varying nominal composition from 90 10 through to 60 40 atom %. The catalysts were prepared using a formic acid reduction method developed by the authors which resulted in very poorly alloyed particles, even after heat treatment to 300 °C under a hydrogen atmosphere. Unfortunately, the authors were not able to obtain Ru K edge data to identify the local structure of the Ru in their catalysts. 

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