Bismuth oxide deposition

Early catalysts for acrolein synthesis were based on cuprous oxide and other heavy metal oxides deposited on inert siHca or alumina supports (39). Later, catalysts more selective for the oxidation of propylene to acrolein and acrolein to acryHc acid were prepared from bismuth, cobalt, kon, nickel, tin salts, and molybdic, molybdic phosphoric, and molybdic siHcic acids. Preferred second-stage catalysts generally are complex oxides containing molybdenum and vanadium. Other components, such as tungsten, copper, tellurium, and arsenic oxides, have been incorporated to increase low temperature activity and productivity (39,45,46). 

Cathodic deposition of bismuth(in) telluride films has been reported [224] also on copper and nickel foils, from aqueous nitric acid solutions of bismuth oxide and tellurium oxide in molar ratios of Bi Te = 3 3 and 4 3, at 298 K. The... 

Arsenic.—The residue of bismuth oxide obtained above is triturated to a fine powder, and dissolved in sulphuric acid with heat. Set a Marsh apparatus in operation, using 20 gm. of arsenic-free, granulated zinc, and dilute (1 5) sulphuric acid, then introduce the bismuth solution in small quantities at a time into the evolution flask. No deposit of arsenic should be visible in the reduction tube within half an hour. 

Decen-l-ol is oxidized by air to 9-decenoic acid in aqueous media in the presence of a supported platinum catalyst with bismuth atoms deposited on the surface of the platinum particles [221]. Metal-supported bismuth catalysts have been studied extensively for selective oxidation of hydrocarbons and alcohols for industrial use [222]. 

M. (2005) Deposition and characterisation of bismuth oxide thin films./. Eur. Ceram. Soc., 25, 2171-2174. 

Zirconia, cerates, or bismuth oxides in very thin solid layers are permeable to ionic forms of hydrogen or oxygen thus, they have been used especially in membrane reactors. In order to obtain significant permeabilities these membranes should be very thin, making it necessary to deposit them on to an appropriate porous support. Other membranes that could be considered dense are obtained by filling a porous membrane with a liquid that remains immobilized and controls permselectivity [13, 14]. 

In Moroccan deposits, cobalt occurs with nickel in the forms of smaltite, skuttemdite, and safflorite. In Canadian deposits, cobalt occurs with silver and bismuth. Smaltite, cobaltite, erythrite, safflorite, linnaeite, and skuttemdite have been identified as occurring in these deposits. AustraUan deposits are associated with nickel, copper, manganese, silver, bismuth, chromium, and tungsten. In these reserves, cobalt occurs as sulfides, arsenides, and oxides. 

The solution should be free from the following, which either interfere or lead to an unsatisfactory deposit silver, mercury, bismuth, selenium, tellurium, arsenic, antimony, tin, molybdenum, gold and the platinum metals, thiocyanate, chloride, oxidising agents such as oxides of nitrogen, or excessive amounts of iron(III), nitrate or nitric acid. Chloride ion is avoided because Cu( I) is stabilised as a chloro-complex and remains in solution to be re-oxidised at the anode unless hydrazinium chloride is added as depolariser. 

In addition to metal alkyls and cyclopentadienyl compounds other types of true organometallic precursors have also been applied in ALD depositions. For example, ( 6115)361 [162,163] and (C6H5)4Pb [164] have been used for the preparation of bismuth- and lead-containing oxide thin films. These compounds are nof exfremely reactive and therefore ozone is needed to obtain completely oxidised films [162,163]. H2O2 as a second precursor does not oxidise (C6H5)3Bi completely, since metallic bismuth was observed in the deposited films [162]. 

These results and the comparison between the catalyst particles before and after catalytic run point out the ability for these particles both to exchange electrons and oxygen anions and to change morphology under the conditions of the catalytic reaction with spreading of the oxides one over the other. These two phenomena should be at the basis of the explanation of synergy effect in molybdates based catalysts. The fact that some FexCoi.xMo04 particles remain free (i.e. not deposited on bismuth molybdate particles) show that even more active and selective catalysts may be obtained in more reliable preparation conditions. 

Impubities.—rhosphorus is rarely adulterated, and the only impurities contained in it are those derived from the acid used in its preparation. Dumas considers flexibility as a characteristic of good phosphorus. Occasionally arsenic, antimony, bismuth, and some other metals have boon found in it. If the acid used contained arsenioua acid, or an oxide of antimony, these are reduced in the process of manufacture of phosphorus, and are found in it in the metallic state. A solution of phosphorus in dilute nitrio acid should give no precipitate with sulphide of hydrogen, and the precipitate procured by a barytic salt should be entirely soluble in excess of nitric acid, proving the absence of sulphur. If arsenic is present, the solution in nitrio acid deposits a black precipitate of metallic arsenic when submitted to evaporation. 

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