Chromium incorporation

Cr-ZSM-5 catalysts prepared by solid-state reaction from different chromium precursors (acetate, chloride, nitrate, sulphate and ammonium dichromate) were studied in the selective ammoxidation of ethylene to acetonitrile. Cr-ZSM-5 catalysts were characterized by chemical analysis, X-ray powder diffraction, FTIR (1500-400 cm 1), N2 physisorption (BET), 27A1 MAS NMR, UV-Visible spectroscopy, NH3-TPD and H2-TPR. For all samples, UV-Visible spectroscopy and H2-TPR results confirmed that both Cr(VI) ions and Cr(III) oxide coexist. TPD of ammonia showed that from the chromium incorporation, it results strong Lewis acid sites formation at the detriment of the initial Bronsted acid sites. The catalyst issued from chromium chloride showed higher activity and selectivity toward acetonitrile. This activity can be assigned to the nature of chromium species formed using this precursor. In general, C r6+ species seem to play a key role in the ammoxidation reaction but Cr203 oxide enhances the deep oxidation. 

Lower activity exhibited by Cu-Cr catalysts can also be attributed to its low surface area and pore volume than those of Cu-based catalysts. In Cu catalysts, CuO and CUAI2O4 are the possible phases which are expected to provide more effective active sites for the oxidation of carbon monoxide. Presence of CuCr204 was reported on Cu-Cr catalysts which were found to be less active if the copper concentration on alumina support was less than 12% by weight.(11). A part of Cr may partly stay on the surface as either Cr species or small crystallites of Cr203(12) on Cu-Cr catalysts and may block the active copper sites. Furthermore, lower activity can also be due to lower surface area and pore volume of the chromium incorporated catalysts. 

Chromium incorporation into MFI structures was also claimed on the basis of IR spectroscopic evidence, i.e., based on the observation of a band aroimd 960 cm [346,347]. The authors of Ref. [347] provided the whole spectrum of the framework vibrations (1500-450 cm ), which they interpreted in line with the work by Flanigen et al. [ 112]. 

Chromium(VI) catalyzes the oxidation of alcohols with alkyl hydroperoxides . Chromium-incorporated molecular sieves, in particular chromium-substituted aluminophosphate-5 (Cr-APO-5) were shown to be effective for the aerobic oxidation of secondary alcohols to the corresponding ketones (Reaction 19). This, and related catalysts, were first believed to be heterogeneous but more detailed investigations revealed that the observed catalysis is due to small amounts of soluble chromium that are leached from the framework by reaction with hydroperoxides. Reaction 19 may involve initial chromium-catalyzed free radical autoxidation of the alcohol to the a-hydroxyalkyl hydroperoxide followed by chromium-catalyzed oxygen transfer with the latter and/or H202 (formed by its dissociation) via an oxochromium(VI)-chromium(IV) cycle. 

Chromium Incorporation Basic Concepts and the YAlOi-YCrOi Case Study 1269... 

Chromium Incorporation Basic CorKepts and the YAlOr-YCrOs Case Study 1273... 

Liu L, Li H (2006) A comparative study on catalytic performances of chromium incorporated and supported mesoporous MSU-x catalysts for the oxidehydrogenation of ethane to ethylene with carbon dioxide. Catal Today 115 235-241... 

N.H. Menzler, de L.G. Haart, D. Sebold, Characterization of cathode chromium incorporation during mid-term stack operation under various operational conditions. ECS Trans. 7(1), 245-254 (2007)... 

Bakers inactive dry yeast is also widely used in the food industry. This yeast may be grown specifically as a food supplement and consequently there is a choice in its composition by varying growth conditions and feedstock makeup. It can possibly produce high levels of nicotinic acid and thiamin, the cmde protein content can be raised to 50—55% and it can be used as a vehicle for the incorporation of micronutrients such as selenium or chromium into the diet. 

Chromium is able to use all of its >d and As electrons to form chemical bonds. It can also display formal oxidation states ranging from Cr(—II) to Cr(VI). The most common and thus most important oxidation states are Cr(II), Cr(III), and Cr(VI). Although most commercial applications have centered around Cr(VI) compounds, environmental concerns and regulations ia the early 1990s suggest that Cr(III) may become increasingly important, especially where the use of Cr(VI) demands reduction and incorporation as Cr(III) ia the product. 

Chromium Surfa.ce Conversion. Converting the surface of an active metal by incorporating a barrier film of complex chromium compounds protects the metal from corrosion, provides an excellent base for subsequent painting, provides a chemical poHsh, and/or colors the metal. 

Figure 12-8A. Piston rings. The piston rod is manufactured from heat-treated stainless steel and is coated with wear-resistant overlays, such as ceramic, chromium oxide, and tungsten carbide applied by plasma techniques. Piston rod cross-head attachment has mechanical preloading system for the threads. Rider rings and seal rings are manufactured from PTFE filled resins fillers are matched to the gas, piston speed, and liner specifications. Typical fillers are glass, carbon, coke, or ceramic. (Used by permission Bui. BCNA-3P100. Howden Process Compressors Incorporated. All rights reserved.)...

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