Barium promotion

Copper chromite 14) and barium-promoted copper chromite (75,/7) have been used for acid reductions but very high temperatures (300 C) are required. The necessary temperature is sufficiently higher than that required foresters to permit selective reduction of half-acid esters to the hydroxy acid 23). The reverse selectivity can be achieved by reduction over H Ru4 CO)a PBu3)4 at I00-200 C and 1500-3000 psig. This homogeneous catalyst will reduce acids and anhydrides, but not esters (2). 

A complex nanostructured catalyst for ammonia synthesis consists of ruthenium nanoclusters dispersed on a boron nitride support (Ru/BN) with barium added as a promoter (33). It was observed that the introduction of barium promoters results in an increase of the catalytic activity by 2—3 orders of magnitude. The multi-phase catalyst was first investigated by means of conventional HRTEM, but this technique did not succeed in identifying a barium-rich phase (34). It was even difficult to determine how the catalyst could be active, because the ruthenium clusters were encapsulated by layers of the boron nitride support. By HRTEM imaging of the catalyst during exposure to ammonia synthesis conditions, it was found that the... 

Another common catalyst prepared by coprecipitation is copper-chromium oxide, also known as "copper chromite" or Adkins catalyst.23 This catalyst is prepared by the addition of copper nitrate to a solution of ammonium dichromate in ammonia giving a precipitate copper ammonium dichromate. This precipitate is filtered, dried and then calcined at 650°-800°C, or more commonly, heated with a flame to induce a thermal reaction (Eqn. 13.5). The resulting fine powder is washed with acetic acid and dried to give the copper chromite catalyst.23 A more active catalyst is prepared by adding 10% barium nitrate by weight of copper before precipitation.24,25 Copper chromite catalysts containing calcium and were found to be less effective than those having a barium promoter.25... 

Yanagisawa, A., Takahashi, H., Aral, T. Reactive barium-promoted Reformatsky-type reaction of a-chloro ketones with aldehydes. Chem. Commun. 2004, 580-581. 

Reactive Barium-promoted Carbon-Carbon Bond-forming Reactions... 

J. Lu, X. Zhang, J. J. Bravo-Suarez, K. K. Bando, S. T. Oyama, Direct propylene epoxidation over barium promoted Au/Ti-TUD catalysts with Hz and Op Effect of Au particle size, J. Catal. doi 10.1016/j.jcat.2007.06.006. 

The bulk composition and the main phases identified with X-ray diffraction are reported in table 1. Quite well crystallized phases on alumina supported catalysts were observed i.e. CuCr204 for unpromoted catalysts and BaCr04 for barium promoted catalysts. Less crystalline solids were obtained when graphite was used as a support. In this case different phases were observed i.e. CuCr02 and CU2O which showed that the support had a significant effect on the bulk composition. ... 

Nitrile conversion in presence of barium promoted Cu-Cr/graphite catalysts. Reaction conditions see table 3. (Catalysts are used without reduction treatment). 

Cyclopropyl propene Copper chromium oxide-barium promoted 100 1,500 2-Cyclopropyl propane 10... 

Difluoropyrrole (58) has been extensively used in the syntheses of octafluor-oporphyrins and other calyx( )pyrroles. This was first accessed by Leroy and Wakselman by barium-promoted copper chromite decarboxylation of 3,4-difluor-opyrrole-2-carboxylic acid in quinoline at 200°C. The acid was prepared in four steps beginning with a cycloaddition reaction of the protected aziridine 59 and chlorotrifluoroethylene (Fig. 3.26). 

Bielawa H, Hinrichsen O, Birkner A, Muhler M. The ammonia-synthesis catalyst of the next generation barium-promoted oxide-supported ruthenium. Angew Chem Int Ed 2001 40 1061-2. 

Lu, J., Zhang, X., Bravo-Suarez, J., et al. (2007). Direct Propylene Epoxidation over Barium-Promoted Au/Ti-TUD Catalysts with H2 and O2 Effect of Au Particle Size, J. Catal., 250, pp. 350-359. 

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