19.2.1 Catalysts preparation
The zirconium-copper mixed oxides were prepared by co-precipitation of hydroxides from mixtures of different salts, using NaOH or KOH as precipitating agent, as presented in Table 19.1. The solids have been dried at 100°C, calcined in air at 400°C (4 h), and in situ activated in H2 (12 h) at a given treatment temperature.
The structure of the oxides during reduction was analyzed in a Siemens D5000 diffractometer equipped with an Anton Paar HTK 10 chamber and connected to a gas introduction and purification line. A position-sensitive detector was used; the experimental conditions were similar to those adopted in Bali et al. (1995). Apart from the Ka2 contribution eliminated by computer post-processing, the patterns obtained were not subjected to further treatments. Owing to the use of a platinum holder, they show platinum diffraction peaks, the evolution of which with TR was taken into account in determining the exact position of the peaks of the solids analyzed.
XPS were registered with a Leybold-hereaus LHS 10 spectrometer, using an Al anode (1486.6 eV) operated at 300 W in a chamber pressure of nearly 1.33 x 10—6 Pa. For calibration of the binding energy scale of the photoemission features, the C 1 s peak at 285 eV was taken as a reference. The reproducibility was +/— 0.2 eV. The samples, pressed on a gold holder, were mounted on a sample rod that permitted reduction treatments (20% H2 in N2) up to 673 K, in a preparation chamber directly connected to the ultra-high vacuum analysis system. They were reduced for 16 h before analysis. The measurements were run at room temperature.
Measurement of the amount of hydrogen stored in the bulk and at the surface in the reduced oxides and the activities in isoprene hydrogenation is based on the ability of this class of solids to hydrogenate 2-methylbuta-1, 3 diene (isoprene) in the absence of gaseous hydrogen at atmospheric pressure, according to a dynamic method described previously (Jalowiecki et al., 1985). The solid is previously in-situ treated in H2 at 250°C (12 h) and the reaction is studied in a temperature range between 80°C and 150°C. The mass of the catalyst is of 50 mg and the partial pressure of isoprene in He is of 19-20 torrs.
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Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.