Oxidation CO and

Carbon forms 2 extremely stable oxides, CO and CO2, 3 oxides of considerably lower stability, C3O2, C5O2 and C]209, and a number of unstable or poorly characterized oxides including C2O, C2O3 and the nonstoichiometric graphite oxide (p. 289). Of these, CO and CO2 are of outstanding importance and their chemistry will be discussed in subsequent paragraphs after a few brief remarks about some of the others. 

Probably the most significant control technology breakthrough came m 1977, when Volvo released a computer-controlled, fuel-mjected vehicle equipped with a three-way catalyst. The new catalytic converters employed platinum, palladium, and rhodium to simultaneously reduce NO and oxidize CO and HC emissions under carefully controlled oxygen conditions. The new Bosch fuel injection system on the vehicle provided the precise air/fuel control necessary for the new catalyst to perform effectively. The combined fuel control and three-way catalyst system served as the foundation for emissions control on the next generation of vehicles. 

These reactions are important in a cycle that oxidizes CO and hydrocarbons and produces ozone, in the presence of NO (NO + N02). In photochemical smog, ozone can build up to... 

Three-way catalysts are able to reduce NO as well as oxidize CO and hydrocarbons when the exhaust composition is held near the stoichiometrically balanced composition, or "stoichiometric point." This control of exhaust composition is accomplished, after the initial warmup period, through the use of the feedback control system illustrated in Figure 1 (2, 3, 4). ... 

Catalytic converters are basically smog control devices on newer automobiles. Catalytic converters have an oxidation catalyst that oxidizes CO and hydrocarbons to CO2 and H2O. It may also have a reduction catalyst that reduces NO to N2. The catalysts involved with these processes are generally platinum or palladium metal operating at relatively high temperature. 

When this happens, the oxygen flux to the particle surface is cut-off because of its consumption in oxidizing CO, and C02 becomes the relevant gasification agent for the particle surface according to the Boudouard Reaction ... 

As the composition of the catalyst changed, the inability to predict the CO/CO2 ratio becomes more and more limiting on the use of the model. The explicit solution was originally applied to the catalyst containing chromia (Cr203) and with relatively poorer diffusivity. With this catalyst and with the operating conditions at that time, the assumption of a constant value of a in each zone was adequate. The chromia was introduced into the catalyst early in the use of the TCC units to oxidize CO and to reduce the concentration of CO in the bottom plenum chamber and in the stack. The presence of too much CO in these parts of the unit could lead... 

The SCR technology is also considered for the control of NO emission in diesel vehicles. Here the SCR catalyst is typically placed after the diesel oxidation catalyst (DOC), which is used to oxidize CO and UHCs and to convert part of the NO to NO2. In this way, the SCR catalysts can take advantage of the fast SCR reaction to enhance significantly the de-NO efficiency at low temperature (Figure 13.4). The fast SCR reaction is based on the following stoichiometry ... 

Indeed, it is possible to install on vehicles a preoxidizing catalyst upstream ofthe SCR catalyst that converts part ofthe NO to NO2 the DOC also oxidizes CO and UHCs to CO2. 

The catalyst, used in the form of a ceramic honeycomb monolith, is constituted, as in mobile applications, by a noble metal and an absorber element, such as potassium, deposited on a Y-AI2O3 wash-coat layer. In the oxidation and absorption cycle, the SCON Ox catalyst works by simultaneously oxidizing CO and UHCs to CO2 and H2O, while NOj, are captured on the adsorber compound. Catalyst regeneration is accomplished by passing a controlled mixture of regeneration gases across the surface of the catalyst in the absence of oxygen. 

Thus, the main function of the DOC is to oxidize CO and unburned HCs. The secondary function, utilized in combined exhaust aftertreatment systems, is the oxidation of NO to N02, which then enables optimum operation of the NOx aftertreatment catalysts placed down the exhaust line (NSRC and/or SCR, cf. Sections VI, VII and VIII, and also DPF). 

The chemistry and function of Rh6(CO)16 and Re2(CO)10 as oxidation catalysts for organic compounds is under continuing investigation. In particular, we are studying the role of Rhe(CO)16 as a labile multisubstrate oxidation catalyst for oxidizing CO and triphenylphosphine (33, 34). 

While both the primary and secondary ozonides have been isolated and characterized, the pair formed by the carbonyl oxide (CO) and the carbonyl compound (CC) has never been directly put into evidence. This elusive intermediate, called also Criegee intermediate zwitterion (CZ), according to this AMI study which did not take into account solvent effects, forms a tight pair or a dipolar complex (DC). The primary ozonide has an O-envelope halfchair conformation and as such two conformers are possible from a rfr-alkene 11 and 12 and only one 13 from the trans-alkene. The splitting of the primary ozonide can lead either to an anti 14 or syn 15 CO and has a determining role for the stereochemical outcome of the reaction <1997JOC2757>. 

The primary photochemical loss process for O3 arises from the sequence of reactions which produces OH, i.e. (R3) and (R5). Tropospheric ozone generation by photochemistry can arise from the oxidation CO and hydrocarbons via reaction sequences such as... 

Fe"Ni Fg and Co Ni" Fg each have a unit cell size that is appropriate for the formulation. In each M there are two O electrons, and the smaller nuclear charges in combination with this, cause the Co and Fe salts to be progressively larger than Ni Ni Fg table I). The cell of Zn Ni Fg is larger than that of Cu Ni Fg because of the four O electrons of Zn. The pure Zn salt is diamagnetic, but with the more easily oxidized Co and Fe compounds there is pronounced field dependence of the magnetism. This correlates with electron-transfer from M to Ni X... 

Direct initiation by either mechanism is characterized by a lack of induction period (47) and is most efficient by metals that are strongly oxidizing (Co and Fe) or can form metal-oxygen complexes (Co and Cu). 

Aluminum oxide clusters having the same stoichiometry as bulk alumina are able to oxidize CO and, subsequently, the reduced cluster can be reoxidized to produce the original active stoichiometry. These findings are relevant to the supply of oxygen to catalyst particles in supported heterogeneous catalysis. 

Carbon forms two common oxides, CO and CO2. It also forms a third (very uncommon) oxide, carbon suboxide, C3O2, which is linear. The structure has terminal oxygen atoms on both ends. Write the Lewis formula for C3O2. 

One of the most widely known examples of catalyst poisoning is taken from the automobile industry. Though tetra-ethyl lead has been removed from essentially all gasoline in North America, the ban on leaded gasoline is not worldwide, and leaded and unleaded gasoline is available in many countries. Catalytic converters, which contain precious metals like platinum, palladium, and rhodium, are used to both reduce NO c and oxidize CO and unburned hydrocarbons. Lead irreversibly destroys the catalytic ability of the converter. Concentrations of lead in leaded gasoline are nominally 150mg/L. 

It was established that ethene oxide, CO and CO2 were formed on Ag-Sup at temperature range of 370-410 K. Such the products were formed at the presence of Ag-Im2, although the reaction took place at more high temperatures (450-500 K). The major product of partial oxidation on Ag-Ph was butene-2,3 oxide. It has been formed begining from 340 K with 100 % selectivity and ethene conversion being of 30-35 % at 408-415 K. The ethene oxide was detected in trace amounts. 

Whereas carbon forms the molecular oxides CO and C02 with multiple bonding (see Topics Cl and C5), stable oxides of Si and Ge are polymeric. Silica Si02 has many structural forms based on networks of corner-sharing Si04 tetrahedra (see Topic D3). Ge02 can crystallize in silica-like structures as well as the rutile structure with six-coordinate Ge. This structure is stable for Si02 only... 

These reactions are important in a cycle that oxidizes CO and hydrocarbons and produces ozone, in the presence of sufficient NO. In photochemical smog, ozone can build up to unhealthy levels of several hundred parts per billion (ppb) as a result of these reactions. There are many other reactions that occur, some of which may be significant at various times, including the destruction of O3 by NO, production and loss of HONO (nitrous oxide) and peroxyacetyl nitrate (PAN), and further oxidation of CH2O. These reactions, and many more, represent a complex set of chemical interactions. For our purposes here, it is only necessary to note the major... 

The converter typically contains 0.15-0.30 g rhodium, which reduces NOx to N2, and 1-2 g platinum, which oxidizes CO and hydrocarbons to CO2 (ref. 5). Palladium is sometimes used in combination with platinum as oxidation catalyst but possible detrimental interactions between Pd and Pt or Rh when they are used together have been reported (ref. 6). 

Second, note that CO and hydrocarbon conversions remain relatively high even at very rich A/F s. The oxygen storage function of the catalyst serves to oxidize CO and hydrocarbons during rich excursions (through stoichiometric reactions with a limited capacity and, thus, limited duration) in the absence of sufficient gaseous oxygen. 

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