Chromia promotion

The oxidative dehydrogenation of ethanolamine to sodium glycinate in 6.2 M NaOH was investigated using unpromoted and chromia promoted skeletal copper catalysts at 433 K and 0.9 MPa. The reaction was first order in ethanolamine concentration and was independent of caustic concentration, stirrer speed and particle size. Unpromoted skeletal copper lost surface area and activity with repeated cycles but a small amount of chromia (ca. 0.4 wt%) resulted in enhanced activity and stability. 

Recently, a novel process for the preparation of chromia promoted skeletal copper catalysts was reported by Ma and Wainwright (8), in which Al was selectively leached from CuA12 alloy particles using 6.1 M NaOH solutions containing different concentrations of sodium chromate. The catalysts had very high surface areas and were very stable in highly concentrated NaOH solutions at temperatures up to 400 K (8, 9). They thus have potential for use in the liquid phase dehydrogenation of aminoalcohols to aminocarboxylic acid salts. 

Table 1 Compositions and surface areas of unpromoted and chromia-promoted skeletal copper catalysts ...

Figure 6 First order rate constants for repeated cycles of ethanolamine dehydrogenation over chromia-promoted skeletal copper catalysts under standard conditions.

Figure 1 shows plots of -ln(l-XH2) versus t for some of the monoalcohols tested, in comparison with ethanolamine, using the chromia-promoted catalyst. The plots are reasonably linear, but with some upward curvature indicating a deviation from first order behaviour at high conversion, in all cases the slopes (i.e. the rate) are less than that for the control ethanolamine. The structures and the first order rate constants, knz, calculated from the slopes in Figure 1 are listed in Table 2. 

Figure 1. First order plots based on hydrogen evolution for the oxidative dehydrogenation of ethanolamine (EA), 2-(2-aminoethylamino)ethanol (AEAE), 3-amino-1-propanol (AP), 2-(methylamino)ethanol (MAE) and benzyl alcohol (BA) over chromia-promoted copper.

Figure 2. First order plots based on hydrogen evolution for the reaction of ethylene glycol (EG), diethanolamine (DEA) and 1,4-butanediol (BD) over unpromoted copper (Cu) and chromia-promoted copper (CrCu).

Figure 4. NMR spectra for a sample taken at 71% conversion during the reaction of diethanolamine over chromia-promoted copper with and without glycine added.

Figure 6. Theoretical dependence of Yheg on k2/ki in comparison with values observed for the reaction of DEA over unpromoted and chromia-promoted copper catalysts...

Unpromoted and chromia-promoted skeletal copper catalysts were prepared as described in detail previously (10, 11, 14, 15) by leaching a CUAI2 alloy, sieved to 106-211pm, in a large excess (500 mL) of 6.1 M NaOH, either alone or containing Na2Cr04 (0.004 M), for 24 hours at 5°C. 

Styrene. All commercial processes use the catalytic dehydrogenation of ethylbenzene for the manufacture of styrene.189 A mixture of steam and ethylbenzene is reacted on a catalyst at about 600°C and usually below atmospheric pressure. These operating conditions are chosen to prevent cracking processes. Side reactions are further suppressed by running the reaction at relatively low conversion levels (50-70%) to obtain styrene yields about 90%. The preferred catalyst is iron oxide and chromia promoted with KzO, the so-called Shell 015 catalyst.190... 

This tutorial paper begins with a short introduction to multicomponent mass transport in porous media. A theoretical development for application to single and multiple reaction systems is presented. Two example problems are solved. The first example is an effectiveness factor calculation for the water-gas shift reaction over a chromia-promoted iron oxide catalyst. The methods applicable to multiple reaction problems are illustrated by solving a steam reformer problem. The need to develop asymptotic methods for application to multiple reaction problems is apparent in this example. 

Two illustrative examples will be discussed. The first example, the chromia-promoted iron oxide catalysis of the water-gas shift reaction, can be solved to engineering accuracy on a hand calculator. The second example, steam reforming of methane over a supported nickel catalyst, involves multiple... 

The chromia-promoted iron oxide catalyzed water-gas shift reaction ... 

Three different CO/CO2 ratios were studied at three different temperatures over chromia-promoted magnetite. Figure 6 presents Langmuir isotherms for the different gas ratios at 637 K. From the small changes in composition of the gas phase upon adsorption, the individual amounts of CO and CO2 adsorbed were measured independently. Figures 7 and 8 show Langmuir isotherms for CO and CO2... 

Summary of Adsorption Site Densities on Chromia-Promoted Magnetite in CO2/CO Gas Mixtures at 637... 

It has been shown that the addition of lead to a chromia-promoted magnetite WGS catalyst enhances the activity for WGS (4 ), A study of the solid state changes which occur upon this substitution was made to probe the active sites..of the catalyst. Through a combination of oxidation studies, Mossbauer spectroscopy, and X-ray diffraction line broadening, a model for the. catalyst was developed. It was concluded that Pb was present as Pb " at tetrahedral sites. The Pb substitution resulted in the expansion of the tetrahedral sites, contraction of the octahedral sites, and the oxidation of some Fe to Fe. The resulting octahedral cations became more covalent in nature, and since the octahedral cations have been reported to be the active sites for CO oxidation over ferrites... 

The stability of the chromia promoted skeletal Cu in highly concentrated caustic solution at temperature around 400K indicates significant potential for use in organic synthesis reactions such as the dehydrogenation of amino alcohols to carboxylic acid salts. 

The results in Table 2 and Figure 7 also indicate that the chromia promoted skeletal Cu catalyst CuCrl retains high BET and Cu surface areas even at temperatures up to 623K. The relatively high thermal stability of the very fine Cu crystallites makes the catalyst suitable for those reactions taking place at higher temperatures, possibly up to 623K. 

Chromia promoted skeletal Cu catalyst, after thermal pretreatment at 623K for 1 hour, has no loss of the Cu surface area, whilst that for an unpromoted skeletal Cu catalyst and a commercial Cu chromite catalyst suffer losses of Cu areas of 3 mV and 4 mV respectively due to Cu sintering. 

M. Tinkle, J. A. Dumesic, Isotopic exchange measurements of the rates of adsorption/desorp-tion and inter conversion of CO and CO2 over chromia-promoted magnetite implications for water-gas shift, J. Catal. 103 (1987) 65-78. 

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