Supported Chromium Oxide

Second, in the early 1950s, Hogan and Bank at Phillips Petroleum Company, discovered (3,4) that ethylene could be catalyticaHy polymerized into a sohd plastic under more moderate conditions at a pressure of 3—4 MPa (435—580 psi) and temperature of 70—100°C, with a catalyst containing chromium oxide supported on siUca (Phillips catalysts). PE resins prepared with these catalysts are linear, highly crystalline polymers of a much higher density of 0.960—0.970 g/cnr (as opposed to 0.920—0.930 g/cnf for LDPE). These resins, or HDPE, are currentiy produced on a large scale, (see Olefin polymers, HIGH DENSITY POLYETHYLENE). 

Low pressure (0.1 to 20 MPa) and temperatures of 50 to 300°C using heterogeneous catalysts such as molybdenum oxide or chromium oxide supported on inorganic carriers to produce high density polyethylene (HDPE), which is more linear in nature, with densities of 0.94 to 0.97 g/cm. ... 

A wide range of nonacidic metal oxides have been examined as catalysts for aromatization and skeletal isomerization. From a mechanistic point of view, chromium oxide catalysts have been, by far, the most thoroughly studied. Reactions over chromium oxide have been carried out either over the pure oxide, or over a catalyst consisting of chromium oxide supported on a carrier, usually alumina. Depending on its history, the alumina can have an acidic function, so that the catalyst as a whole then has a duel function character. However, in this section, we propose only briefly to outline, for comparison with the metal catalyzed reactions described in previous sections, those reactions where the acidic catalyst function is negligible. 

Earlier work in this laboratory showed that chromium oxide supported on alumina is a good catalyst for the conversion of olefins (ref. 1) as well as paraffins (ref. 2) to nitriles with high selectivities, by reaction of NO with the hydrocarbons (nitroxidation). Recent work (ref. 3) reported preliminary results of the nitroxidation of paraxylene as an extension of the use of C Oj-Al Oj to the catalytic synthesis of aromatic nitriles. It should be mentioned that only few data are available in the literature related to the nitroxidation of aromatic hydrocarbons. Teichner et al (ref. 4 ) reported interesting results of selective synthesis of benzonitrile by nitroxidation of toluene on NiO-AlgO catalysts. Improvements of the catalytic activity and selectivity in this reaction were reached by use of C Og-Al. which also exhibits striking properties in the synthesis of paratolunitrile by contact of NO with paraxylene (ref. 3). 

The high dehydrogenation activity observed for Cr3 sa-montmorillonite almost certainly arises from the facile accessibility of the chromium oxide aggregates supported in the clay gallery. Substantial contribution to the observed activity due to active sites at the external surfaces of the mineral is precluded by the virtual absence of activity for the Cr1 88 derivative. Thus, Cr3 53-montmorillonite behaves catalytically much like bulk chromium oxide supported on alumina (17) ... 

Alcohols may be oxidized in a similar way. However, these reactions strongly resemble those reported for Cr molecular sieves, and a small concentration of Cr in solution may well account for most of the observations of catalysis. Binary molybdenum-chromium oxides supported on alumina have been used in the autoxidation of cyclohexene with 02 and r-BuOOH as an initiator (62). This is a complex reaction in which uncatalyzed and Cr-catalyzed oxidation combine to yield 2-cyclohexen-l-one, 2-cyclohexen-l-ol, and 2-cyclohexenyl hydroperoxide the Mo compound can use the hydroperoxide formed in situ as an oxidant for the epoxidation of cyclohexene. Although much lower oxygen consumption was observed for the reaction filtrate than for the suspension, it is unclear how the Cr is held by the oxide. 

Rgune 20 Raman spectra of 4% chromium oxide supported on alumina, titania, and silica. 

In a Claus plant plant H2S is converted into sulfur however, the conversion is not complete (94-98%). About 1% H2S and 0.5% COS remain in the off-gas due to the thermodynamics of the Claus equilibrium reaction. Van Nisselrooy and Lagas [162] developed a catalytic process, called Superclaus, which is based on bulk sulfur removal in a conventional Claus section, followed by selective catalytic oxidation of the remaining H2S to elemental sulfur. Iron oxides and chromium oxides supported... 

Commercial linear polyethylene, the most commonly used type of plastic, was bom more than half a century ago with the accidental discovery at Phillips Petroleum Company that chromium oxide supported on silica can polymerize a-olefins.1 The same catalyst system, modified and evolved, is used even today by dozens of companies throughout the world, and it accounts for a large share of the world s high-density polyethylene (HDPE) supply, as well as some low-density polymers. The catalyst is now more active and has been tailored in numerous ways for many specialized modem applications. This chapter provides a review of our understanding of the complex chemistry associated with this catalyst system, and it also provides examples of how the chemistry has been exploited commercially. It is written from an industrial perspective, drawing especially on the commercial experience and the research of numerous scientists working at Phillips Petroleum... 

The characterization of the surface of supported metal oxide catalysts is vital to the understanding of many catalytic reactions. Supported chromium oxide catalysts are used for many industrial catalytic processes. Chromium oxide supported on alumina is used as a catalyst for propane and butane dehydrogenation. " Determination of the surface structure under reaction conditions is important for a complete understanding of the catalyst system. 

A competitor of Phillips catalyst, based on chromium oxide supported on silica, is the Union Carbide catalyst, which is prepared by the reaction of chromocene with silica. When chromocene, [Cp2Cr ], reacts with SiO2-(800)> it gives [(=SiO)Cr(Cp)] according to mass balance analysis (Scheme 42 and Table 12), and this surface complex is highly active in ethylene polymerization. ... 

The effect of a wide range of feed concentration of PCE from 30 to 10,000 ppm on the stability of chromium oxide supported on Ti02 and AI2O3 for the removal of chlorinated volatile organic compounds (CVOCs) has been investigated over a fixed bed flow reactor. Both chromium oxide catalysts exhibited stable PCE removal activity up to 100 h of reaction time without any catalyst deactivation when 30 ppm was introduced into the reactor. 

The high-pressure process relied on large and complex plants that required careful process control. Therefore, the discovery in 1953 of the appropriate catalysts that allowed the process to be carried under low pressure ( 500 psi) was welcomed by the industry [7]. Three types of catalysts were developed about that time the Ziegler-type catalysts typically obtained by reacting alkyl aluminum compounds with titanium chloride metal oxide catalyst systems, developed by Phillips Petroleum in the United States, typically made of chromium oxide supported on a silicaceous carrier [8]) and a different type of oxide catalyst developed by Standard Oil Company. The first plants based on the Ziegler catalyst went on line in Germany by 1955 and a plant based on the Phillips catalyst in Texas opened in 1957. The third catalyst system developed much slower and was picked up by the Japanese plastics industry in a plant opened in 1961. 

Zhang X, Yue Y, Gao Z (2002) Chromium oxide supported on mesoporous SBA-15 as propane dehydrogenation and oxidative dehydrogenation catalysts. Catal Lett 83 19-25... 

Michorczyk P, Ogonowski J, Kustrowski P, Chmielarz L (2008) Chromium oxide supported on MCM-41 as a highly active and selective catalyst for dehydrogenation of propane with CO2. Appl Catal Gen 349 62-69... 

Hardcasde FD, Wachs IE Raman spectroscopy of chromium oxide supported on alumina, titania, and sUica a comparative study, J Mol Catal 46(1—3) 173—186, 1988. 

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