Iron catalyst, amorphous

CO oxidation, 28 108 iron catalyst, 30 168 kinetics, 28 250-257 complicated, 28 257-263 latest developments in, 5 1 over amorphous metal alloys, 36 372-374 over iron, 36 24-25 on alumina support, 36 47 antipathetic behavior, 36 150, 152 particle size and, 36 131-132 promotion by potassium, 36 36-37 over rhenium. 36 24-25 promotion by potassium, 36 37 photocatalysis over perovskites, 36 304 Anunoxidation, 30 136-137 allyl alcohol, 30 157-158... 

First attempts to check this hypothesis [23] revealed a superior catalytic activity of iron in amorphous iron-zirconium alloys in ammonia synthesis compared to the same iron surface exposed in crystalline conventional catalysts. A detailed analysis of the effect subsequently revealed that the alloy, under catalytic conditions, was not amorphous but crystallized into platelets of metastable epsilon-iron supported on Zr-oxide [24, 25]. 

Figure 5.7 Three-dimensional drawing of the experimental system used to assess the catalytic properties of the amorphous iron silicate smokes. The (smoke) catalyst is contained in the bottom of a quartz finger (attached to a 2L Pyrex bulb) that can be heated to a controlled temperature. A Pyrex tube brings reactive gas to the bottom of the finger. The gas then passes through the catalyst into the upper reservoir of the bulb and flows through a copper tube at room temperature to a glass-walled observation cell (with ZnSe windows) in an P iiR spectrometer. From there, a closed-cycle metal bellows pump returns the sample via a second 2L bulb and the Pyrex tube to the bottom of the catalyst finger to start the cycle over again (Hill and Nuth 2003).

Four iron catalysts promoted with varying amounts of potassium were reacted at 215°C in synthesis gas for 24 h and then tested using TPSR. The results of the experiments are shown in Figure 6, which tabulates the quantities of amorphous CHx carbon, carbidic, and graphitic carbon found on each catalyst. The most graphite formed on the unpromoted iron... 

Peak 5 can be assigned on the basis of previous work with Ni and Ru catalysts to amorphous coke or Cp. The formation of a hydrogen-containing carbon species during CO hydrogenation has been verified on Ru [18] and iron catalysts [13]. While Dwyer observed no polymethylene, as he calls it, on K-fiee iron after reaction for 8 hours at 7 atm, H2/CO = 3 and 540 K, identical treatment of a catalyst promoted with potassium produced a multilayer coverage of Cp. Accordingly, the area of Peak 5 should increase with K addition. Indeed, upon the addition of K... 

Source of Activity in other Siliceous Catalysts.—Although various oxides can be combined with silica to give amorphous, acidic catalysts, the replacement of aluminium in zeolites (specially non-faujasitic zeolites) has proved to be very difficult with any element other than gallium. Materials of ZSM-5 structure with iron or boron in place of aluminium have been claimed recently, but it is not yet certain that either iron or boron is part of the zeolite lattice or that the catalytic activity observed is not due to residual lattice aluminium. 

CFCs were decomposed to HCl, HF, and CO2 at 150 °C to 350 °C by the reaction of H2O over amorphous alloy catalysts consisting of at least one element selected from the group of Ni and Co, at least one element selected from the group Nb, Ta, Ti, and Zr, and at least one element selected from the group Ru, Rh, Pd, Ir, and Pt. The alloys were activated by immersion in HF [105]. CFCs are decomposed by the reaction of water vapor at temperatures above 300 °C in the presence of iron oxide supported on activated carbon [106]. They are also decomposed by steam in... 

The conversion of acetylene on an iron catalyst on Si02-support is a typical example. In this process, acetylene is thermally decomposed by leading it over a bed of catalyst within a quartz tube heated at about 700 °C (500-1000 °C, generally). Apart from the desired MWNT, there are also larger, fibrous structures and layers of amorphous graphene observed. These tend to coat the catalyst particles. The bamboo-like nanotubes (Section 3.3.4) usually obtained from this method are often covered with amorphous carbon too and, in parts, they are considerably curved. In addition to these bent species, there is also a spiral or helical structure... 

Soot, or amorphous carbon, is the material that remains upon decomposition of hydrocarbons. Though it has long been known that soot is produced during the decomposition of hydrocarbons over Fe catalysts, it wasn t until 1953 that Davis, Slawson and Rigby also observed the presence of carbon fibers (20). These fibers existed within a sample of amorphous carbon that formed from the decomposition of CO at Fe surfaces. These fibers were described as worm-like structures that form during the decomposition of CO at about 450°C in the presence of Fe. The iron could be small iron particles present in, or even in macroscopic iron samples. It was clear that the Fe played the role of catalyst in the formation of these carbon stractures. Today, the process of growing carbon nanotubes from the decomposition of a hydrocarbon precursor at an iron catalysts is conunoirly known as thermal chemical vapor deposition (CVD). 

Studying non-classical preparation procedures, it has been already shown that ultrasound play a relevant role in preparing high dispersed pure amorphous iron [3]. Moreover, it has been recently proposed that ultrasound can improve the metal dispersion in alumina supported ruthenium catalyst 14, 51. 

Crystal Structure. The fused iron catalyst is not a single crystal phase, but a mixture, which is made up of two or more crystal phases and amorphous phases. In addition, the pores should be taken as a separate phase. The crystal compounds are the basic components of fused iron catalyst. 

Rayment T. made a meaningful test that the powder catalyst was reduced with sky-high space velocity at 450°C and atmospheric pressure, so that the concentration of water vapor was reduced to the level of difficult to measure by conventional methods. It is found from X-ray diffraction result that the catalyst after reduction mainly is not a-Fe, but amorphous iron with very high activity. Naturally, this method cannot be applied in industry. 

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