Hydrocarbons oxidative activation

Figure 16 shows that hydrocarbon oxidation activity decreases logarithmically with the lead content of noble metal catalysts. Activity of these... 

Fig. 15. Comparison of the deterioration of methane oxidation activity with total hydrocarbon oxidation activity at 500°C. Lead level in fuel is 0.05 g/gal. [From Shelef et al. (10).]...

Effect of Alkaline Addition on Hydrocarbon Oxidation Activities of Palladium Three-way Catalyst... 

This paper systematically reports the effect of alkaline addition, that is, alkali metals and alkaline earth metals, on hydrocarbon oxidation activity of Pd three-way catalyst. 

The conversions of HC, CO, and NOx on the Pd and Pd/Sr catalysts plotted as a function of X in simulated exhaust gases at 300°C are shown in Figs.l and 2, respectively. The catalytic activity on the Pd/Sr catalyst was superior to that on the Pd catalyst, in particular, under reducing conditions defined as A.<1. The conversion of HC, as representation of hydrocarbon oxidation activity, on the catalysts with alkaline earth metals and that with alkali metals plotted as a function of X in simulated exhaust gases are shown in Figs.3 and 4,... 

The alkaline earth metal addition to the Pd catalyst improved the hydrocarbon oxidation activity. Similar phenomena have been observed on Pd/Ba and Pd/La catalysts, and it is concluded that the suppression of hydrocarbon chemisorption on Pd by the addition of Ba or La allows the catalytic reaction to proceed smoothly under reducing conditions( 16,20). On the other hand, the alkali metal addition, especially K or Cs, to the Pd catalyst deteriorated the hydrocarbon oxidation activity. 

In C3HJ-O2 reaction system, the hydrocarbon oxidation activity on the Pd catalysts with alkaline compound was measured to get further information. The rate of carbon dioxide formation V(C02) in the reaction of CjHg with O2 is given by the following equation (1). 

The relationship between the partial reaction order m and the hydrocarbon oxidation activity in the simulated reducing automotive exhaust gas at A.=0.98 are shown in Fig. 5. It was found that the maximum order of m was a certain negative one(-0.6), that is, the hydrocarbon oxidation activity increased with increasing the order of m from -1.39 to -0.6 and decreased with increasing the order of m further than -0.6. 

The effect of alkaline addition on the hydrocarbon oxidation activity of Pd catalyst loaded on y-alumina was investigated using simulated exhaust gases. The hydrocarbon oxidation activity of Pd catalyst with alkaline earth metal such as Mg, Ca, Sr, and Ba is higher than that with nothing added. On the other hand, the activity of Pd catalyst with alkali metal such as K and Cs is lower than that with nothing added. 

Major improvements in hydrocarbon oxidation activity and overall thermal durability were achieved through the use of more palladium-rich formulations as lead disappeared from the fuel supply. Palladium is highly prone to lead-based deactivation. The dramatic increase in palladium in the late 1990s caused a significant supply-demand imbalance in the PGM markets in 2000, driving up palladium prices tenfold. The recent effort to reduce requirements for palladium without affecting hydrocarbon performance restored the market balance. 

A similar plot of hydrocarbon oxidation activity is presented in Figure 6. The activity-composition relations reflect a more extreme sensitivity of pure palladium toward lead in hydrocarbon oxidation than was observed in CO oxidation (cf. Figure 5). The difference between pal-... 

We decided to evaluate the catalytic activity on a honeycomb of the best base metal catalyst that we know of in the absence of sulfur (a severe poison). If under the best conditions we could not provide sufficient catalytic activity (60% hydrocarbon oxidation activity in a typical... 

Table I. Relative Hydrocarbon Oxidation Activities of Various Oxides...

A cell-free, soluble enzyme preparation of a Pseudomonad bacterium strain, isolated from soiP", has been found to oxidize octane to n-octanol and octanoic acid. Pyridine nucleotide, oxygen and Fe ions are involved in this bioconversion. The reaction has been studied at 28 °C with a system consisting of buffer, octane(specific activity 5 X lO cpm/imol" ) dissolved in EtOH or acetone, enzyme and suitable cofactors. The reaction could be stopped by the addition of dilute H2SO4. Suitable work-up of the system yielded unreacted " C-octane, " C-octanol and " C-octanoate, respectively. The sum of the radioactivity found in octanol and octanoate served as a measure of the hydrocarbon-oxidizing activity of the enzyme system since the intermediates (hydroperoxide, octanal) do not accumulate. 

Upon exposure to higher p02 at SOFC temperatures, the cmiductivity decreases slowly [96]. This is observed in Fig. 3.19 as the significant decrease in conductivity for all of the samples as the /7O2 is increased above 10 " atm. The slow kinetics associated with this may be related to slow cation diffusion [101] and/or low oxygen mobility in these materials [103]. Slow reoxidation kinetics are beneficial to application in the SOFC anode where accidental and occasional exposure of the anode material to air may be expected. Of course, this assumes that a suitable and cost-effective cell synthesis procedure can be derived to initially form these highly conductive states. Furthermore, slow reoxidation may indicate slow surface oxygen exchange and low hydrocarbon oxidation activity. 

Extraordinarily effective promotion by electropositive modifiers (alkalies or alkaline earths) of Pt-group metals (Pd, Pt, and Rh) during reactions related to TWCs has been firstly reported by Yentekakis, Lambert, and coworkers at the end of 1990s [39-44]. Indeed, it has been shown that the CO and hydrocarbons oxidation activity, but more importantly the de-NO activity and N2-selectivity, of noble metals can be substantially enhanced by alkali or alkaline earths. For example Pt, the noble metal mostly studied in this turn, demonstrated an enhancement on NO reduction rate by up to two orders of magnitude accompanied by a notable increase of N2-selectivity upon optimal promotion by Li, Na, K,... 

Finocchio, E. and Busca, G. (2001). Characterization and hydrocarbon oxidation activity of coprecipitated mixed oxides Mn304/Al203, Catal. Today, 70, pp. 13-225. 

High carbon monoxide and hydrocarbon oxidation activity at a low engine temperature. 

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