Reduction catalysts

Before use the new or regenerated catalyst is reduced in dry hydrogen at 500 t at a space velocity of 400 h for about 2 h. This converts the platiniun oxides into finely divided metal particles. 

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Reduction of sulfur dioxide by methane is the basis of an Allied process for converting by-product sulfur dioxide to sulfur (232). The reaction is carried out in the gas phase over a catalyst. Reduction of sulfur dioxide to sulfur by carbon in the form of coal has been developed as the Resox process (233). The reduction, which is conducted at 550—800°C, appears to be promoted by the simultaneous reaction of the coal with steam. The reduction of sulfur dioxide by carbon monoxide tends to give carbonyl sulfide [463-58-1] rather than sulfur over cobalt molybdate, but special catalysts, eg, lanthanum titanate, have the abiUty to direct the reaction toward producing sulfur (234). 

Fig. 13. Flowsheet of medium pressure synthesis, fixed-bed reactor (Lurgi-Ruhrchemie-Sasol) having process conditions for SASOL I of an alkaline, precipitated-iron catalyst, reduction degree 20—25% having a catalyst charge of 32—36 t, at 220—255°C and 2.48 MPa (360 psig) at a fresh feed rate of...

High yields of optically active cyanohydrins have been prepared from hydrogen cyanide and carbonyl compounds using an enzyme as catalyst. Reduction of these optically active cyanohydrins with lithium aluminum hydride in ether affords the corresponding substituted, optically active ethanolamine (5) (see Alkanolamines). 

Cu/ Zn0/Si02 catalyst obtained with different doses of 5 keV Ne" ions (see insert, spectra are shifted vertically for clarity). Catalyst reduction temperature 700 K. Solid lines fitted Gauss peaks [3.147]. (b) The relative coverage of Cu and ZnO on the silica-supported catalyst, reduced at 700 K, as a function of the ion dose [3.147]. 

The minimal amount of 4 that allows efficient coupling with 5 as substrate was determined (Table 5). This amount, a little over 0.25 molar equivalents relative to the substrate, implies that all four protons of 4 participate in the catalyst reduction process. 

The reduction of this ester over Pd differed from the corresponding reaction over Pi in every important particular. Enantiomeric excess was low (high over Pt) and in the reverse sense (e g cinchonidine modification provided an S-excess in the product over Pd but an R-excess over Pt) Enantioselective reactions underwent self-poisoning over Pd (proceeded to completion over Pt), were of non-integral order (integral over Pt) and proceeded more slowly than reaction over unmodified catalyst (enhanced rate over Pt) Enantioselective reaction was solvent-specific over Pd (not over Pt) and was favoured by low catalyst reduction temperature (high reduction temperature for Pt)... 

It has been shown that on Cu-ZSM-5 and Cu-ZrOj catalysts, reduction of NO and NOj in the presence oflarge excess of Oj proceed at about the same rate [20,21]. This is because over these catalysts, NO2 is rapidly reduced to NO (and not NO being rapidly oxidized to NOj) [20,22,23]. On the other hand, on catalysts that do not contain transition metal ions, such as Na-ZSM-5 [24], GajOj [25], AljO, [26], and H-ZSM-5 [26], NO2 reduction to Nj proceeds much... 

Recent work done by Xiong et al.84 on Co/AC (activated carbon) catalysts showed that a Co2C species formed during the catalyst reduction in hydrogen at 500°C. Evidence for the carbide in the Co/AC catalysts was obtained by x-ray diffraction and XPS measurements, and the formation of this Co2C species reduced the FTS activity over the Co-based catalysts. The presence of bulk carbide also seems to enhance alcohol selectivity.85... 

Catalyst Reduction Temperature pmol H2 Desorbed Uncorrected... 

Catalyst/Reductant(s) Solvent Temperature [K] TONb) TOFc) [h-1] Reference... 

In summary, the reduction of ketones and aldehydes can both be performed with MPV and transition-metal complexes as catalysts. Reductions of alkenes, al-kynes, and imines require transition-metal catalysts MPV reductions with these substrates are not possible. 

The first step in this reaction mechanism is the catalyst reduction. Cat-0 represents an oxidized catalyst, which is attacked by a reductant (Red). The catalyst itself undergoes reduction, while the... 

As with methanol desorption, a net weight loss was observed for the FeHo catalyst after ammonia desorption. This was caused by oxidation of the ammonia substrate to nitrogen and consequent catalyst reduction. The relative number of oxygen atoms removed was ca. 20 less than with methanol surface reduction. 

Figure 4. The effect of catalyst reduction in deoxygenation of ethyl stearate. Reaction conditions 5 mol% ethyl stearate in hexadecane, T = 270 °C, p = 1 bar, nicat = 0.4 g and liquid flow rate (V ) =0.1 ml/min.

A novel method for production of paraffinic hydrocarbons, suitable as diesel fuel, from renewable resources was illustrated. The fatty acid ethyl ester, ethyl stearate, was successfully converted with high catalyst activity and high selectivity towards formation of the desired product, heptadecane. Investigation of the impact of catalyst reduction showed that the reduction pretreatment had a beneficial effect on the formation of desired diesel compound. The non-pretreated catalyst dehydrogenated ethyl stearate to ethyl oleate. The experiments at different reaction temperatures, depicted that conversion of ethyl stearate was strongly dependent on reaction temperature with Eact=69 kj/mole, while product selectivities were almost constant. Complete conversion of ethyl stearate and very high selectivity towards desired product (95%) were achieved at 360°C. 

Dynamic ETEM experiments on CS defects have shown mat mey consume anion vacancies and grow (figure 3.7). These correlation studies indicate mat CS planes are secondary or detrimental to catalytic reactivity. They eliminate anion vacancies by accommodating the supersaturation of the vacancies in the reacting oxide catalyst and me catalyst reactivity (selectivity) begins to decrease with the onset of CS formation, i.e. CS planes are the consequence of catalyst reduction reactions rather than the origins of catalytic reactivity (Gai 1981,1992, 1993, Gai etfl/ 1982). 

In the nickel- and cobalt-catalysed reactions [166,207] it was observed that the butene distribution depended upon the temperature of reduction of the catalyst. For both powders and alumina-supported catalysts prepared by reduction of the oxides, reduction at temperatures below ca. 330° C gave catalysts which exhibited so-called Type A behaviour where but-2-ene was the major product and the frans-but-2-ene/cis-but-2-ene ratio was around unity. Reduction above 360° C (Ni) or 440° C (Co) yielded catalysts which gave frans-but-2-ene as the major product (Type B behaviour). It is of interest to note that the yield of cis-but-2-ene was not significantly dependent upon the catalyst reduction temperature with either metal. 

The reaction between propene and the catalyst is, in general, rate-determining, as catalyst reoxidation is a relatively fast reaction. This implies that the degree of catalyst reduction under steady state reaction conditions is fairly low (i.e. less than 10% with respect to the total amount of oxygen that can be removed with propene). Thus the observed kinetics... 

Pulse experiments have been carried out by Sancier et al. [276], who tried to avoid the problem of non-stationary conditions by seasoning of the catalyst by ]602/propene pulses, followed by the actual experiment with 1802/propene pulses. ESR measurements confirmed that the degree of catalyst reduction was indeed constant. The ]80/160 ratio in the prod-... 

The activity of an oxide catalyst in the absence of gas phase oxygen provides direct evidence that lattice oxygen can perform the selective oxidation process, although it does not exclude the possibility that, in the presence of gas phase oxygen, other forms of oxygen also participate in some stage of the reaction. Pulse experiments are the most suitable for this purpose, because rapid catalyst reduction is then avoided. As pulse experiments have been amply reviewed in Sect. 2, only the conclusions will be discussed here. 

Catalytic investigations were performed in a glass flow apparatus at atmospheric pressure. Appropriate pretreatment and catalyst reduction for each catalytic reaction was carried out. 

Conjugate reduction. Silicon hydrides and a Pd(0) catalyst reductively cleave allylic acetates selectively (equation I).1... 

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