CO formation rate

C02 hydrogenation on Pd was investigated29 under atmospheric pressure and at temperatures 540°C to 605°C. The CO formation rate (reverse water-gas shift reaction) exhibits purely electrophilic behaviour with a rate increase by up to 600% with increasing sodium coverage (Fig. 9.20). This purely electrophilic behaviour is consistent with low reactant coverages and enhanced electron acceptor C02 adsorption on the Pd surface with increasing sodium coverage (Rule G2). 

Fig. 4. Effect of pinluile diameter on gaseous formation rates ai on carbon selectivity O, energy efficiency basal on LHV A, aietgy efficiency based on HHV , uqnit power 9, H2 formation rate A, CO formation rate gap distaiKe 6.0 mm QjHsOH cone., 50 mol% diaphragm fhickness, 1.0 mm.

Fig. 11. CO formation rates determined from reactant conversions and product selectivities in a fixed-bed flow reactor for C02 reforming of CH4. The catalysts were nickel supported on La203, y-Al203, or CaO. Each catalyst contained 17 wt% Ni. Before reaction, the catalyst was reduced in flowing H2 at 773 K for at least 5 h and then at 1023 K for 2 h. Reaction conditions pressure, 1.0 atm temperature, 1023 K feed gas molar ratio, CH4/C02/He = 2/2/6 GHSV, 1,800,000 mL (g catalyst)-1 h-1 (227).

In all experiments, the major products were ethane and carbon dioxide. Under some conditions, ethylene and carbon monoxide were also observed. In the following, Rj is the C] products (CO2 and CO) formation rate, and R2 is the C2 products (C2H6 and C2H4) formation rate. The methane conversion is defined as (Rj+2R2)/CH4 in feed. The selectivity to C2 products is defined as 2R2/(Ri+2R2), while the C2 yield is defined as the product of conversion and selectivity. Our experimental results indicate that methane does react with carbon dioxide to produce carbon monoxide and either hydrogen or water under reaction conditions, but if oxygen is present, most of the carbon monoxide will be further oxidized to... 

Plotting CO formation rate versus the formaldehyde concentration of the reaction mixture an irregular behaviour was observed. In fact CO can be formed via... 

Results from this model show that the early presence of a significant amount of H2 boosts the CH and hence the CO formation rates. However, the H2 is unstable against collisional dissociation and is essentially destroyed on some characteristic timescale t,] after which time the CO abundance is frozen as in the basic model. Reducing the initial ejecta temperature results in a slower CO formation rate as before but it also has the effect of increasing the "lifetime of the pre-existent H2 (t ) since the H2 collisional dissociation reaction ... 

To explain the experimental facts (no carbon deposition, CO formation rate always higher than the formation rate of ethylene), the authors suggested that two catalyzed reactions are taking place ... 

The hydrogenation of CO and C02 on transition metal surfaces is a promising area for using NEMCA to affect rates and selectivities. In a recent study of C02 hydrogenation on Rh,59 where the products were mainly CH and CO, under atmospheric pressure and at temperatures 300 to 500°C it was found that CH4 formation is electrophobic (Fig. 8.54a) while CO formation is electrophilic (Fig. 8.54b). Enhancement factor A values up to 220 were... 

Figure 10.7. CO2 formation rate from CO and O2 over Rh(l 11) and Rh(l 10) surfaces [Adapted from M. Bowker, Q. Guo, and R.W. Joyner, Catal. Lett. 18 (1993) 119]. Note the similarity to the simple model used to describe the rate in Fig. 2.12.

Study of the Co(III) oxidation of Cl has been restricted to observation of the CoCP intermediate complex and measurement of its formation rate -... 

Figure 5 summarises results for the CO2, N2 and N2O formation rates for the dependence of apparent activation energies on catalyst potential. Although there is a notable increase in activation energy with increased Na coverage in each case, the variation is not as abrupt at that characteristic of EP CO oxidation [24] and NO+CO reactions. 

Overall, we demonstrated electrode potential- and time-dependent properties of the atop CO adsorbate generated from the formic acid decomposition process at three potentials, and addressed the issues of formic acid reactivity and poisoning [Samjeske and Osawa, 2005 Chen et al., 2003,2006]. There is also a consistency with the previous kinetic data obtained by electrochemical methods the maximum in formic acid decomposition rates was obtained at —0.025 V vs. Ag/AgCl or 0.25 V vs. RHE (cf. Fig. 12.7 in [Lu et al., 1999]). However, the exact path towards the CO formation is not clear, as the main reaction is the oxidation of the HCOOH molecule ... 

Figure 3.9. Transient C02 formation rates on Pd30 (a) and Pd8 (b) mass-selected clusters deposited on a MgO(lOO) film at different reaction temperatures [74]. In these experiments CO was dosed from the gas background while NO was dosed via a pulsed nozzle molecular beam source. The turnover frequencies (TOFs) calculated from the experiments displayed in (a) and (b) are displayed in the last panel (c). C02 formation starts at lower temperatures but reaches lower maximum rates on the larger cluster. (Figure provided by Professor Heiz and reproduced with permission from Elsevier, Copyright 2005).

The authors further tested the Pt(l 11) and Pd(l 10) surfaces [71, 72] using in situ STM and SXRD. All these single crystals show a similar kinetic behavior in CO oxidation. The gradual roughening of the surface corresponds to the formation of surface oxides and a higher CO oxidation rate. The structure insensitivity observed at high pressure is in contrast with the results obtained in UHV, where the reactivity shows a strong orientational dependence. 

For instance, Cr(III) ions may coexist with Co(II) and Cu(II) ions in a complex sample. The latter two ions may produce CL emission under similar conditions as for Cr(III). Fortunately, the formation rate of the Cr-EDTA complex is relatively slower, making possible the selective determination of this metal ion in waste water [8], urine, blood, and hair [9], Owing to the small number of CL reagents explored in recent years, the elements covered by CL techniques are still rather limited. Up to now only a few elements have been found to produce direct CL emission when reacted with CL reagents. Most of the publications so far involve indirect methods for the detection of elements. 

Ruthenium carbonyl decomposes the formate ion in basic media, but at a rate slower than the rate of the WGSR. At 100° and 0.10 mM Rug(C0)] 2 under 3 atm N2> the rate of decomposition of trimethyl ammonium formate to H2 and CO2 is 0.6 mmol/hr. Under 5 atm CO the rate is slower (<0.1 mmol/hr), but the overall rate of H2 production is >0.4 mnol/hr. At this low CO pressure, the rate of H2 production directly from CO and H2O is more than three times that from formate decomposition. Furthermore, since increases in CO pressure result in improved H2 production rates (10 mnol/hr at 50 atm CO), while apparently inhibiting the rate of formate decomposition, it may be concluded that formate decomposition has little mechanistic significance in the WGSR activity of Ru (CO)... 

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