Catalyst samples preparation

Some of the catalyst samples prepared were characterized by EPR and XPS. EPR spectra were recorded at 20 and -196°C using a JE0L JES-FE3X spectrometer. XPS measurements were taken by using a VG ESCA 3 spectrometer with an aluminium radiation source. All binding energies were referred to the A12p line (BE = 74.7 eV). 

Giro et al. (1986) measured hole mobilities of PVK prepared with different catalysts. Samples prepared with different catalysts show essentially the same mobilities. The mobilities were thermally activated with activation energies that increase with decreasing field. It was speculated that the low mobilities, relative to trap-free values of 10-3 cm2/Vs reported by Reimer and Bhssler (1979) and Fujino et al. (1982,1982a, 1984), were due to impurities originating during the polymerization process and linked to the main polymer chain and structural faults. 

It is already observed that the selectivity to products formation of main reaction is significantly smaller on the catalyst sample prepared by immersion in solution of the highest Ni concentration. 

Catalyst samples prepared by contacting sample B in its finally reduced form with water (designated B-H20) or with a chloroiridic acid solution (designated B-lr), followed by drying and reduction steps identical to those employed in the preparation of the original sample B. 

There is reason to believe that catalyst samples prepared in different laboratories may not be identical, despite the best efforts to make them so. The most likely differences between samples are probably due to differences in adsorption properties, which are rarely well identified during catalyst characterization. Yet differences in adsorption equilibrium constants can lead to great variability in kinetic and selectivity behaviours, even in simple catalytic rate expressions, as we have just seen. 

The EPR spectra recorded at 120K of the Sn02-Cu catalyst sample prepared by impregnation (a) as prepared and (b) after calcination at 600° show that a single Cu2+ species with a cylindrical enviromnent is present in each case although with differing g and A values. At intennediate calcination temperatures both species exist. Wlien a compositionally identical sample prepared by coprecipitation is examined, both species are observed in the freshly prepared sample even prior to calcination. 

Catalyst samples prepared by impregnation and precipitation-deposition were tested in order to estimate their activity for the CO2 reforming of methane. Both catalysts were active and stable, but the Ni-PD catalyst was more active. 

A belief sometimes expressed by catalysis chemists is that this particular catalyst is not active unless there is present some chromium in a higher oxidation state. The presence of such oxidized chromium is readily detected by extraction of the sample with water, followed by titration of the extract with ferrous ammonium sulfate solution, followed by back titration with standard dichromate. All such tests on the catalyst samples prepared as described above were negative. Chromium in a higher oxidation state is, however, always present if the final step of reduction in hydrogen is omitted. 

The chromium/zeolite catalyst sample prepared by ion exchange with a Cr concentration of 0.6% was studied by ciclic votametry and ESR spectroscopy. 

Reduction of 17a-EthynyI to 17a-Ethyl °° A solution of 5 g of 17a-ethynyl-androst-5-ene-3j9,17j5-diol in 170 ml of absolute alcohol is hydrogenated at atmospheric pressure and room temperature using 0.5 g of 5 % palladium-on-charcoal catalyst. Hydrogen absorption is complete in about 8 min with the absorption of 2 moles. After removal of the catalyst by filtration, the solvent is evaporated under reduced pressure and the residue is crystallized from ethyl acetate. Three crops of 17a-ethylandrost-5-ene-3) ,17j9-diol are obtained 3.05 g, mp 197-200° 1.59 g, mp 198.6-200.6° and 0.34 g, mp 196-199° (total yield 5.02 g, 90%). A sample prepared for analysis by recrystallization from ethyl acetate melts at 200.6-202.4° [aj, —70° (diox.). 

MgO-supported model Mo—Pd catalysts have been prepared from the bimetallic cluster [Mo2Pd2 /z3-CO)2(/r-CO)4(PPh3)2() -C2H )2 (Fig. 70) and monometallic precursors. Each supported sample was treated in H2 at various temperatures to form metallic palladium, and characterized by chemisorption of H2, CO, and O2, transmission electron microscopy, TPD of adsorbed CO, and EXAFS. The data showed that the presence of molybdenum in the bimetallic precursor helped to maintain the palladium in a highly dispersed form. In contrast, the sample prepared from the monometallie precursors was characterized by larger palladium particles and by weaker Mo—Pd interactions. ... 

The prepared catalysts were characterized by x-ray diffraction (XRD), N2 adsorption and CO chemisorption. Also, X-ray absorption spectroscopy (XAS) at the Ni K edge (8.333 keV) of reference and catalyst samples was carried out in the energy range 8.233 to 9.283 keV at beamline X18B of the... 

It is true that these X-ray procedures are much less sensitive to sample preparation them chemisorption techniques. Nonetheless, it is desirable to use them in conjunction with such methods. In analysis of chemisorption data, it is necessary to make an assumption as to the number of gas molecules that attach to each atom in the catalyst. 

In perovskite-type catalysts the formation of the final phase is completed already at 973 K. XRD and skeletal FTIR/FTFIR data for LalCol, LalMnl and LalFel calcined at 973 K evidence that only LalFel-973 is actually monophasic and consists of a perovskite-type phase with orthorombic structure. A perovskite type phase with hexagonal-rombohedral structure represents the main phase of LalCol-973, but traces of C03O4 and La2C05 are also present. In the case of LalMnl-973 two phases have been detected both with perovskite-type structure, one orthorombic and the other rombohedral. The calculated cell parameters of the dominant perovskite-type phase are reported in Table 1 for the three samples. The results compare well with those reported in the literature [JCPDS 37-1493, 32-484, 25-1060] which refer to similar samples prepared via solid state reartion. All the perovskite-type samples are markedly sintered... 

A NaY zeolite (Al/Si atomic ratio 0.41) was supplied by Shokubai Kasei Kogyo Ltd. After an evacuation at 673 K for 1 h (lx 10 Pa), the zeolite powder was exposed to a vapor of Mo(CO)5 or Co(CO)jNO at room temperature, followed by an evacuation at room temperature for 10 min to remove physisorbed metal carlxrnyl molecules on the external surface of the zeolite. Mo(CO)yNaY or Co(CO)3NO/NaY was sulfided in a stream of an atmospheric pressure of 10% HjS/Hj (0.2 dm min ). The sulfidation temperature was increased from room temperature to 373 K at a rate of 2 K min and kept at the tempeiatiue for 1 h. Subsequently, the temperature was increased up to 673 K at a rate of 5 K min and kept at 673 K for 1.5 h. After the sulfidation, the sample was cooled in the HjS/Hj stream to room temperature. The Mo and Co sulfide catalysts thus prepared are denoted MoSx/NaY and CoSx/NaY, respectively. Mo sulfide catalysts, MoSj/NaY, were also prepared by a conventional impregnation method by using ammonium heptamolybdate, for companson. 

We thank Ms. Wei-Chee Tan for the preparation of the catalyst samples. This work was supported by the National Science Foundation (CTS-9403199), the international cooperative program NSF-CONICET (INT-9415590), and the Exxon Education Foundation We thank the University of Mar del Plata for a fellowship (WEA), as part of the international exchange program sponsored by the University of Oklahoma and the University of Mar del Plata. 

---