Platinum reaction with hydrogen

Reaction with Hydrogen and Metals. Bromine combines directiy with hydrogen at elevated temperatures and this is the basis for the commercial production of hydrogen bromide [10036-10-6]. Heated charcoal and finely divided platinum metals are catalysts for the reaction (17). 

Fig. 26. STM images of the oxygen pre-covered platinum(l 1 1) surface during reaction with hydrogen. Images were recorded at a temperature of T = 111 K with a time interval of 625 K. The white ring in the upper right corner is associated with a reaction front of OH intermediates from the autocatalytic reaction. The outside is characterized by an oxygen-terminated surface, whereas water molecules from the reaction are identified inside the ring. Adapted with permission from Reference (757).

C-Tracer studies of acetylene adsorption on alumina- and silica-sup-ported palladium [53,65], platinum [66] and rhodium [53] show the coexistence of at least two adsorbed states, one of which is retained on the surface, the other being reactive undergoing molecular exchange and reaction with hydrogen. Acetylene adsorption exhibits the same general characteristics as those observed with ethylene (see Sect. 3.2). However, there are important differences. The extent of adsorption and retention is substantially greater with acetylene than with ethylene. Furthermore, the amounts of acetylene retained by clean and ethylene-precovered sur-... 

Alkenes can be converted to alkanes by their reaction with hydrogen over a finely divided metal catalyst such as palladium, nickel, or platinum (Following fig.). This is an addition reaction, as it involves the addition of hydrogen atoms to each end of the double bond. It is also called a catalytic hydrogenation or a reduction reaction. 

Benzene undergoes an addition reaction with hydrogen with a platinum/rhodium catalyst at 2-3 atm pressure and at 30°C. 

SAFETY PROFILE Poison by inhalation and ingestion. A corrosive irritant to skin, eyes, and mucous membranes. Inhalation may cause pulmonary edema and hemorrhage. Potentially explosive reaction with acetone + platinum. Mixtures with hydrogen + oxygen ignite spontaneously. When heated to decomposition it emits very toxic fumes of CT and NO. ... 

In a galvanic cell, the cathode consists of a Ag (1.00 M) Ag half-cell. The anode is a platinum wire, with hydrogen bubbling over it at 1.00-atm pressure, that is immersed in a buffer solution containing benzoic acid and sodium benzoate. The concentration of benzoic acid (C5H5COOH) is 0.10 M, and that of benzoate ion (CSH5COO ) is 0.050 M. The overall cell reaction is then... 

In cases not readily amenable to direct chemisorption, titration of specific sites is possible with probe reactions. The reaction must be an irreversible interaction between a gas and surface site, such that only one event occurs per site. The first example of this technique was the titration of Pt-O sites. The surface of supported platinum is first oxidized to form no more than a monolayer. Then follows reaction with hydrogen... 

The formation of a platinum oxide surface layer as given in Eq. (20.6) prevents dissolution or precipitation of platinum according to Eq. (20.5), since dissolution of platinum oxide as shown by Eq. (20.7) is rather slow [14, 15]. Precipitation of Pt + ions by reaction with hydrogen may occur within the membrane, forming an electrically insulated Pt band [16]. Platinum losing electrical contact with the electrode is referred to as catalyst islanding [17]. The electrochemically active platinum surface area decreases because of these mechanisms, resulting in performance... 

On reaction with hydrogen gas with a platinum catalyst, ribose (Problem 5.54) is converted into ribitol. Is ribitol optically active or inactive Explain. 

Activation of hydrogen peroxide has been achieved by the use of methyltrioxorhe-nium (MTO) [322]. Strukul and coworkers employed cationic platinum complexes as catalysts and hydrogen peroxide as the oxidant in the conversion of cyclohexanones into caprolactones [323]. A niobiocene complex has been applied giving esters with a regioselectivity opposite to that generally observed [324]. Some supported platinum [325], nickel [326] and methyltrioxorhenium [327] catalysts have also been used in reactions with hydrogen peroxide. 

The subsequent reduction of the nitrogen to anunonia may proceed by a mechanism similar to that proposed for the dimeric titanium complex [133]. Also the reactions of some arylazo-platinum complexes with hydrogen are suggestive [134], viz. ... 

Place a solution of 10 -4 g. of benzalacetophenone, m.p. 57° (Section IV,130) in 75 ml. of pure ethyl acetate (Section 11,47,15) in the reaction bottle of the catalytic hydrogenation apparatus and add 0 2 g. of Adams platinum oxide catalyst (for full experimental details, see Section 111,150). Displace the air with hydrogen, and shake the mixture with hydrogen until 0 05 mol is absorbed (10-25 minutes). Filter oflF the platinum, and remove the ethyl acetate by distillation. RecrystaUise the residual benzylacetophenone from about 12 ml. of alcohol. The yield of pure product, m.p. 73°, is 9 g. 

Another group of reactions with the predominant cleavage of the ring comprises catalytic hydrogenation of isoxazole derivatives and has been investigated only recently. The most commonly used catalyst has been Raney nickel,but use has sometimes been made of platinum catalysts. Hydrogenolysis of the 0—N bond (172—>173) occurs in isoxazole, its homologs,and their functional derivatives, for example, isoxazole carboxylic acids- and 5-aminoisoxazoles. ... 

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