Carbon monoxide oxidation chromium oxide catalyst

In order to substantiate this measure of chromia area, the rates of carbon monoxide oxidation over the various catalysts were measured. It was found that the alumina portion of the surface could be rendered inactive by selective poisoning with water and, under these conditions, the reaction was catalyzed exclusively by the ehromia surface. Since the activation energy was independent of the chromium content, it was reasonable to expect a linear variation of specific activity (i.e., activity per unit total surface area) with the fraction 0 (Table I) of the total surface contributed by the chromia phase. In Fig. 3 the specific rate is... 

The widely investigated Phillips catalyst, which is alkyl free, can be prepared by impregnating a silica-alumina (87 13 composition [101-103] or a silica support with an aqueous solution of Cr03). High surface supports with about 400 to 600 g/m are used [104]. After the water is removed, the powdery catalyst is fluidized and activated by a stream of dry air at temperatures of 400 to 800 °C to remove the bound water. The impregnated catalysts contain 1 to 5wt% chromium oxides. When this catalyst is heated in the presence of carbon monoxide, a more active catalyst is obtained [105]. The Phillips catalyst specifically catalyzes the polymerization of ethene to high-density polyethene. To obtain poly ethene of lower crystallinity, copolymers with known amounts of an a-olefin, usually several percent of 1-butene ean be synthesized. The polymerization can be carried out by a solution, slurry, or gas-phase (vapor phase) process. 

Reforming is completed in a secondary reformer, where air is added both to elevate the temperature by partial combustion of the gas stream and to produce the 3 1 H2 N2 ratio downstream of the shift converter as is required for ammonia synthesis. The water gas shift converter then produces more H2 from carbon monoxide and water. A low temperature shift process using a zinc—chromium—copper oxide catalyst has replaced the earlier iron oxide-catalyzed high temperature system. The majority of the CO2 is then removed. 

Chromium Oxide-Based Catalysts. Chromium oxide-based catalysts were originally developed by Phillips Petroleum Company for the manufacture of HDPE resins subsequendy, they have been modified for ethylene—a-olefin copolymerisation reactions (10). These catalysts use a mixed sihca—titania support containing from 2 to 20 wt % of Ti. After the deposition of chromium species onto the support, the catalyst is first oxidised by an oxygen—air mixture and then reduced at increased temperatures with carbon monoxide. The catalyst systems used for ethylene copolymerisation consist of sohd catalysts and co-catalysts, ie, triaLkylboron or trialkyl aluminum compounds. Ethylene—a-olefin copolymers produced with these catalysts have very broad molecular weight distributions, characterised by M.Jin the 12—35 and MER in the 80—200 range. 

Methanol Synthesis. Methanol has been manufactured on an industrial scale by the cataly2ed reaction of carbon monoxide and hydrogen since 1924. The high pressure processes, which utili2e 2inc oxide—chromium oxide catalysts, are operated above 20 MPa (200 atm) and temperatures of 300—400°C. The catalyst contains approximately 72 wt % 2inc oxide, 22 wt % chromium (II) oxide, 1 wt % carbon, and 0.1 wt % chromium (VI) the balance is materials lost on heating. 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

The feed to the shift converter contains large amounts of carbon monoxide which should be oxidized. An iron catalyst promoted with chromium oxide is used at a temperature range of 425-500°C to enhance the oxidation. 

Mirkin and coworkers reported on catalytic molecular tweezers used in the asymmetric ring opening of cyclohexene oxide. In this case the early transition metal is the catalyst and rhodium functions as the structural inductor metal. The catalyst consists of two chromium salen complexes, the reaction is known to be bimetallic, and a switchable rhodium complex, using carbon monoxide as the switch. Indeed, when the salens are forced in dose proximity in the absence of CO the rate is twice as high and the effect is reversible [77]. 

Such reactions comprise practically all those in which hydrogen is linked to carbon to produce of necessity hydroxy compounds, which are of industrial importance, e.g., the manufacture of methanol and higher alcohols from carbon monoxide and hydrogen in presence of catalysts, such as zinc-chromium oxides. 

Carbon monoxide and hydrogen, heated under pressure in the presence of a suitable catalyst, combine to form methyl alcohol. A mixture of zinc oxide and chromium oxide has been used as a... 

Catalytic conversion of l-Octanol-2-d to ketone A quantity (29.7 ml.) of l-octanol-2-d was charged (space velocity 0.2) to a 5-mm. reactor tube containing 18 ml. of 8- to 10-mesh chromium oxide catalyst maintained at 400°. The 27.7 ml. of liquid product was fractionated in a concentric-tube etjlumn. A 60.6% yield of di-n-heptyl ketone was obtained. Approximately 17% of the alcohol was recovered "unconverted. Mass spectrometric analysis of the gaseous product showed the atomic ratio of deuterium to hydrogen to be 0.106. The molal yields of deuterium, hydrogen, and carbon monoxide produced per mole of ketone were 0.216, 2.040, and 0.815 respectively. 

The typical Phillips catalyst comprises chemically anchored chromium species on a silica support. The formation of a surface silyl chromate, and eventually silyl dichromate [scheme (29)], is significant during the catalyst preparation, because at the calcination temperature chromium trioxide would decompose to lower-valent oxides. Chromium trioxide probably binds to the silica as the chromate initially, at least for the ordinary 1% loading. However, some rearrangement to the dichromate at high temperature may occur. It is incorrect to regard only one particular valence state of chromium as the only one capable of catalysing ethylene polymerisation. On the commercial CrOs/silica catalyst the predominant active species after reduction by ethylene or carbon monoxide [scheme (59)] is probably Cr(II), but other species, particularly Cr(III), may also polymerise ethylene under certain conditions ... 

The catalysts were evaluated by exposure to a simulated automobile exhaust gas stream composed of 0.2% isopentane, 2% carbon monoxide, 4% oxygen and a balance of nitrogen. The temperature required to oxidize the isopentane and carbon monoxide was used to compare catalyst performance. The chromium-promoted catalyst oxidized isopentane at the lowest temperature, and a mixed chromium/copper-promoted catalyst proved the most efficient for oxidizing carbon monoxide and isopentane. It is interesting to note that the test rig used a stationary engine with 21 pounds of catalyst. Although the catalyst was very effective it is difficult to envisage uranium oxide catalysts employed for emission control of mobile sources. 

After activation, the catalyst is intrcxiuced into the polymerization reactor as slurry in a saturated hydrocarbon such as isobutane. The precise mechanism of initiation is not known, but is believed to involve oxidation-reduction reactions between ethylene and chromium, resulting in formation of chromium (II) which is the precursor for the active center. Polymerization is initially slow, possibly because oxidation products coordinate with (and block) active centers. Consequently, standard Phillips catalysts typically exhibit an induction period. The typical kinetic profile for a Phillips catalyst is shown in curve C of Figure 3.1. If the catalyst is pre-reduced by carbon monoxide, the induction period is not observed. Unlike Ziegler-Natta and most single site catalysts, no cocatalyst is required for standard Phillips catalysts. Molecular weight distribution of the polymer is broad because of the variety of active centers. 

Iron-chromium oxide catalysts, reduced with hydrogen-containing in the conversion plants, permit reactions temperatures of 350 to 380°C (high temperature conversion), the carbon monoxide content in the reaction gas is thereby reduced to ca. 3 to 4% by volume. Since, these catalysts are sensitive to impurities, cobalt- and molybdenum-(sulfide)-containing catalysts are used for gas mixtures with high sulfur contents. With copper oxide/zinc oxide catalysts the reaction proceeds at 200 to 250°C (low temperature conversion) and carbon monoxide contents of below 0.3% by volume are attained. This catalyst, in contrast to the iron oxide/chromium oxide high temperature conversion catalyst, is, however, very sensitive to sulfur compounds, which must be present in concentrations of less than 0.1 ppm. 

In the presence of catalysts such as are used for the synthesis of methanol from mixtures of hydrogen and carbon monoxide and which have been promoted by the addition of an alkali oxide, ethanol may be dehydrated to form butanol in a high pressure process. Catalyst mixtures composed of chromium and zinc oxides to which either barium hydroxide or potassium oxide has been added have been specified.6 ... 

In the proposed vapor phase processes for organic acid synthesis, carbon monoxide is passed with the vaporized aliphatic alcohol over catalysts similar in nature to those employed in the pressure synthesis of higher alcohols from hydrogen-carbon monoxide mixtures. Pressures on the order of 200 atmospheres are employed. Temperatures of about 200° to 300° C. are preferred but it is necessary to use somewhat higher ones in order to obtain sufficient reaction. Mixtures of the oxides of zinc and chromium or copper, promoted with alkali or alkaline earth oxides, are suitable catalysts for the formation of carbon-carbon linkages.97 Catalysts composed of an alkali, chromium, and molybdenum have been claimed for the synthesis of mixtures of higher alcohols, aldehydes, acids, esters, etc., from carbon monoxide and vaporized aliphatic alcohols as methanol, ethanol, etc., at temperatures of about 420° C. and a pressure of 200 atmospheres.98... 

Since methanol is a direct reaction product of hydrogen and carbon monoxide, it is theoretically possible by using an excess of carbon monoxide in the original water gas mixture to form first methanol and then acetic acid or ester in one operation. With this end in view, catalysts composed of metals or their compounds, i.e. of nickel, chromium, cobalt, copper, cadmium, or manganese, have been patented.1"4 Catalysts similar to those proposed for the carbon monoxide-methanol reaction and comprising the oxides of copper, tin, lead, the acetate of copper, or tire methylates of aluminum or tin, or mixtures have been claimed for the same reaction at pressures of 150 to 200 atmospheres and at about 300° C.1 4e... 

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