Al2O3 catalyst

Figure 1 is a TEM photograph of the Cu (10wt%)/Al2O3 catalyst prepared by water-alcohol method, showing the dispersed state of copper and was confirmed the particle sizes from XRD data. Figure 2 is X-ray diffraction patterns of above-mention catalysts, was used to obtain information about phases and the particle size of prepared catalysts. Metal oxide is the active species in this reaction. Particle sizes were determined fix)m the width of the XRD peaks by the Debye-Scherrer equation. 

The catalytic tests show that, over the Pt(l 0 0)/Al2O3 catalyst, the formation of CO and NH3 is largely prevented, whereas the yield of N2O increases compared with the Pt(polycrystalline)/Al203 catalyst. These main differences observed should be ascribed to the morphological differences between two catalysts, i.e., the dominant orientation of the crystallographic facets and the average size... 

Steinfeld et al. [133] demonstrated the technical feasibility of solar decomposition of methane using a reactor with a fluidized bed of catalyst particulates. Experimentation was conducted at the Paul Scherrer Institute (PSI, Switzerland) solar furnace delivering up to 15 kW with a peak concentration ratio of 3500 sun. A quartz reactor (diameter 2 cm) with a fluidized bed of Ni (90%)/Al2O3 catalyst and alumina grains was positioned in the focus of the solar furnace. The direct irradiation of the catalyst provided effective heat transfer to the reaction zone. The temperature was maintained below 577°C to prevent rapid deactivation of the catalyst. The outlet gas composition corresponded to 40% conversion of methane to H2 in a single pass. Concentrated solar radiation was used as a source of high-temperature process heat for the production of hydrogen and filamentous... 

The capability of NO to reduce nitrates, providing a pathway for the production of ammonium nitrite and thus of nitrogen, has also been demonstrated recently by Weitz and co-workers, mainly on the basis of IR data collected over BaNa-Y zeolite [75] however, according to a parallel additional route NO would also react with NO2 to form N2O3 and then nitrogen [reactions (13.25) and (13.26)], as already discussed. The oxidation of NO by surface nitrates over a Pt-Ba/Al2O3 catalyst has also been reported by Olsson et al. [76], whereas the formation of surface nitrates from NO2 on bare AI2O3 has been reported by Apostolescu et al. [77] and previously observed in our laboratories also [78]. 

This work has recently been extended, again with a single Pd/Al2O3 catalyst pellet 69). The image time was reduced to 34 s by introduction of manganese ions into the... 

Recently, Sederman and co-workers (755) used the DEPT MRI pulse sequence described in Section V.A.2 to investigate 1-octene hydrogenation occurring over a l-wt.% Pd/Al2O3 catalyst in a trickle-bed reactor. The reactor was of inner diameter... 

The beneficial effects of sulphur (a few p.p.m. in the feed) on Pt reforming catalysts (lower initial activity but enhanced lifetime and stability, less coking) were reviewed in the earlier Report and further examples have appeared. A selectively sulphided Pt(0.25)-Re(0.25)-Q(1.0)/Al2O3 catalyst with S/Re atomic ratio 0.93 was more active and longer-lived in the reforming... 

Since electrical conductivity reflects the mobility of electrons in the bulk solid (14), the data in Table 2 can be used to compare the amount of mobile electrons in each sample. Table 3 shows the amount of excess mobile electrons (in conductivity unit) of the catalysts shown in table 2. The value (B-A) is the electrical conductivity of 0.3wt%Sn added to Y-AI2O3 support. The value (D-C) is the electrical conductivity of 0.3wt%Sn added to 0.3%Pt/y-Al2O3 catalyst. If Sn does not have any electronic effect on the Pt site, the value (B-A) should be equal to the value (D-C). The calculation, however, clearly indicates that 0.3wt%Sn loaded on 0.3%Pt/y-AI2O3 catalyst does provide more mobile electrons to the catalyst than its presence on y-Al203 support. The addition of alkali metals also shows an interesting result. The value (E-D) is the increase in electrical conductivity of 0.3%Pt-0.3%Sn/y-Al203 after 0.6wt% of the alkali metals was added. The result demonstrates that the alkali metals greatly increase the amount of the excess mobile electrons in the bulk catalysts. 

Figure 1 shows the influence of velocity of alkane feed on the aromatic hydrocarbons yield over 0.35%Pt-0.35%Re/Al2O3 catalyst. Maximum yield of benzene was observed at 2.8-4 h velocity of n-hexane feed. The yield of toluene in this range is 20-23%. Total yield of aromatic hydrocarbons and benzene sharply declined at 5.5 h velocity of n-hexane feed. Optimum volume velocity of hexane feed is in the range 3-4 h. The n-hexane conversion under these conditions reached 87-95%. 

In the case of Pd/Al2O3 catalysts the morphology of the metal particles is also important because it determines the hydrogenation and isomerization selectivity. On flat metal surfaces isomerization is prefened whereas rough surfaces are more active... 

Moreover, the comparison of the respective contributions of bond shift and cyclic mechanism in the isomerization of several labeled and C, hydrocarbons on 10% Pt/Al2O3 catalysts (Table III) shows that the contribution of bond shift to the overall isomerization process decreases with an increase in the number of carbon atoms, but not to the same extent for methyl shift and chain lengthening. Thus, on going from methylpentanes to... 

A more careful study of the hydrogenolysis of methylcyclopentane on two catalysts of extreme dispersion (0.2 and 10% Pt) showed that, in the temperature range 250°-310°C, the product distributions were temperature insensitive on the 0.2% Pt/Al2O3 catalyst, but temperature sensitive on the 10% Pt/AljOj catalyst (86). On the latter, all the observed distributions appeared as combinations of two limiting distributions, one of which includes only methylpentanes and therefore corresponds to a completely selective hydrogenolysis of—CH2—CH2— bonds the other one contains n-hexane, but is different from the one obtained on the 0.2% Pt/Al2O3 catalyst. Platinum films are intermediate between the two types of supported catalysts (86,87. ... 

The initial formation, from isopropylcyclopentane, of ethylcyclopentane, 1-methyl-l-ethylcyclopentane, and ethylbenzene on platinum films or Pt/Al2O3 catalysts 68, 131), illustrates these points concerning the metallocyclobutane mechanism and carbene-olefin addition (Scheme 64). 

More recently, it was found that the hydroxylation state of the alumina has a determining influence upon the particle size of platinum crystallites. Controlled dehydroxylation of the alumina proved to be the most reliable method for preparing stable catalysts with gradual variations of the dispersion, and a continuous series of Pt/Al2O3 catalysts with dispersions (characterized by the H/Pt ratio) ranging from 0.04 to 1.0 was prepared by... 

The most striking result obtained with the series of Pt/Al2O3 catalysts with various dispersions was the constancy (18 + 3%) of the contribution of the cyclic mechanism on all the catalysts of low and medium dispersion (H/Pt... 

Investigation of the Origins of Selectivity in Ethylene Epoxidation on Promoted and Unpromoted Ag/a-Al2O3 Catalysts A Detailed Kinetic, Mechanistic and Adsorptive Study... 

The Detailed Kinetics of the Adsorption and Desorption of Ethylene on an Oxidised Ag/a-Al2O3 Catalyst Subtending the... 

FIGURE 7.1 The temperature-programmed desorption (TPD) spectra of O2 from an Ag/a-Al2O3 catalyst O2 dosing, O2 101 kPa, 25 cmVmin, I h, 513 K. 

Origins of Selectivity in Ethylene Epoxidation on Ag/a-Al2O3 Catalysts... 

FIGURE 7.4 The temperature-programmed desorption (TPD) spectrum of O2 from the Ag/a-Al2O3 catalyst subtending the / -O state principally on the surface. 

In the absence of additives, Ag/a-Al2O3 catalysts typically produce selectivities in the conversion of ethylene to EO of 50%. The addition of the promoters, Cs and Cl in combination, increases the selectivity to 80-85%. The use of Cl as a promoter alone increases the selectivity from 50 to < 75% while their combined use raises the overall selectivity to 85%. The Cl promoter is added continuously from the gas phase. The Cs promoter is added during the catalyst preparation. We shall deal first with Cs promotion because of its simplicity and because it allows for an unambiguous definition of the role of the Cl promoter. 

The effect of that Cs loading was studied by O2 TPD and by ethylene temperature-programmed reaction [3]. The O2 desorption spectrum obtained by Atkins and co-workers for the Cs/Ag/v-AhOa catalyst is shown in Fig. 7.9, lower curve. The upper curve with two peak maxima at 523 K (250 °C) and 573 K (300 °C) is that shown previously for O2 desorption from a fresh, unpromoted Ag/a-Al2O3 catalyst (Fig. 7.1). 

The third step is the heart of the process (steam reformer). Ni-based (Ni-Al2O3) catalysts, loaded in tubular reactors, favour the advancement of the following reactions ... 

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