Catalyst samples preparation reaction conditions

Fig. 5. Removal of NOx over V2O5 catalysts. Circles and squares show results of the catalysts prepared from VO3 -adsorbing unmodified and APS-modified Ti02 samples, respectively. Reaction conditions are described in the Experimental section.

The catalyst electrode has been prepared in a way that the acrolein conversion in the cell was kept below 10 % in any case. Thus the measured potential difference between the electrodes is characteristic for the catalyst under the reaction conditions at the corresponding sample port of the tubular reactor. 

Suitable reagents for derivatizing specific functional groups are summarized in Table 8.21. Many of the reactions and reagents are the familiar ones used in qualitative analysis for the characterization of organic compounds by physical means. Alcohols are converted to esters by reaction with an acid chloride in the presence of a base catalyst (e.g., pyridine, tertiary amine, etc). If the alcohol is to be recovered after the separation, then a derivative which is fairly easy to hydrolyze, such as p-nltrophenylcarbonate, is convenient. If the sample contains labile groups, phenylurethane derivatives can be prepared under very mild reaction conditions. Alcohols in aqueous solution can be derivatized with 3,5-dinitrobenzoyl chloride. 

The reactions with ruthenium carbonyl catalysts were carried out in pressurized stainless steel reactors glass liners had little effect on the activity. When trimethylamine is used as base, Ru3(CO) 2> H Ru4(CO) 2 an< H2Ru4(CO)i3 lead to nearly identical activities if the rate is normalized to the solution concentration of ruthenium. These results suggest that the same active species is formed under operating conditions from each of these catalyst precursors. The ambient pressure infrared spectrum of a typical catalyst solution (prepared from Ru3(CO)i2> trimethylamine, water, and tetrahydrofuran and sampled from the reactor) is relatively simple (vq q 2080(w), 2020(s), 1997(s), 1965(sh) and 1958(m) cm ). However, the spectrum depends on the concentration of ruthenium in solution. The use of Na2C(>3 as base leads to comparable spectra. 

The comparison of catalytic properties was made under identical reaction conditions, among three important candidate catalysts, namely, the Pt/y-Al203, Au/a-Fe203, and Cu Ce, x02 y systems [50], The catalytic tests were performed in the reactant feed containing CO, H2, C02, and HzO — the so-called reformate fuel. The effects of the presence of both C02 and H20 in the reactant feed on the catalytic performance (activity and selectivity) of these catalysts as well as their stability with time under reaction conditions have been studied. The composition of the prepared samples and their BET specific surface areas are presented in Table 7.6. The results obtained with the three catalysts in the presence of 15 vol% COz and of both 15 vol% COz and 10 vol% H20 in the reactant feed (with contact time wcat/v = 0.144 g sec/cm3 and X = 2.5) are shown in Figure 7.12. For comparison, the corresponding curves obtained under the same conditions but without water vapor in the feed are also shown in Figure 7.12. 

Recently, we reported that an Fe supported zeolite (FeHY-1) shows high activity for acidic reactions such as toluene disproportionation and resid hydrocracking in the presence of H2S [1,2]. Investigations using electron spin resonance (ESR), Fourier transform infrared spectroscopy (FT-IR), MiJssbauer and transmission electron microscopy (TEM) revealed that superfine ferric oxide cluster interacts with the zeolite framework in the super-cage of Y-type zeolites [3,4]. Furthermore, we reported change in physicochemical properties and catalytic activities for toluene disproportionation during the sample preparation period[5]. It was revealed that the activation of the catalyst was closely related with interaction between the iron cluster and the zeolite framework. In this work, we will report the effect of preparation conditions on the physicochemical properties and activity for toluene disproportionation in the presence of 82. ... 

Fig. 7. Schematic representation of the preparation and application of catalyst samples for MAS NMR investigations under hatch reaction conditions.

In more recently introduced equipment, the calcination and loading of the catalyst samples can be performed under shallow-bed conditions. For example, the equipment developed by Zhang et al. (51) (Fig. 9) allows a calcination of the powder in a horizontal tube inside a heater at temperatures of up to 1000 K. After loading of the catalyst with probe molecules or reactants, the powder is added to an MAS NMR rotor at the bottom of the equipment, sealed with a rotor cap from a plug rack, and transferred to the NMR spectrometer. As in the case of the former approaches, the samples prepared in the equipment of Zhang et al. 151) can be used for ex situ as well as in situ NMR investigations under batch reaction conditions. Furthermore, this equipment is suitable for ex situ investigations of solid-catalyzed reactions under flow conditions. In this case, the horizontal tube inside the heater is used as a fixed-bed reactor. 

Considering the various approaches of solid-state NMR spectroscopy, contrasting advantages and limitations must be mentioned for batch and flow techniques. MAS NMR spectroscopy under batch reaction conditions with glass inserts for the preparation of the catalyst samples has the advantage that all the materials and equipment are commercially available. Because the amounts of reactants necessary for these experiments are small, only low costs for isotopically enriched materials... 

Finally, we have not discussed cases where Raman spectroscopy can be used to study catalysts indirectly, as for example, by extracting a sample from a reactor and preparing a KBr disc for IR or Raman investigation. Such techniques may be useful in special circumstances (50) but have limited applicability with regard to the direct examination of surfaces under reaction conditions. 

Reactions of organic compounds over solid catalysts are sometimes accompanied by the formation of heavy by-products which can form a deposit on the surface and lead to catalyst deactivation. For o-xylene oxidation the formation of such compounds has been frequently mentioned [15-17] but no information can be found about their influence on the catalyst deactivation. The present work reports on the formation of carbonaceous deposits over V2O5/T1O2 catalysts used for o-xyletie oxidation. Samples prepared by wet impregnation were used under operating conditions that can lead to the formation of heavy compounds. They were then collected and analysed by FTIR and TFO. The present data help to elucidate the characteristics of such compounds and their influence on the catalytic behaviour. 

Dent et al., 1995 Sankar et al., 2000) or with UV-vis spectroscopy of functioning catalysts. In most cases, separate experiments will have to be conducted, and then it is essential to match as exactly as possible the sample, preparation method, and reaction conditions. 

Thiophene HDS was performed at 673 K in a microflow reactor with on-line gas chromatography (GC) analysis. The catalyst samples (200 mg) were pre-sulfided in situ using conditions described in the preparation section. The reaction mixture consisting of 4.0 mol% thiophene in H2 was fed through the reactor and was analyzed every 35 min (flow rate 50 ml min , 673 K, 1 bar). First order rate constants for thiophene conversion to hydrocarbons (Khds) and the consecutive hydrogenation of butene (knyo) were calculated as described elsewhere [8]. 

Zeolite beta samples with different framework and extraframework composition have been prepared by submitting the acid form of a commercial TEA-beta sample to different post-synthesis treatments, i.e. steam calcination, acid (HCl) leaching, and ammonium hexafluorosilicate (HFS) treatment. The samples were characterized by XRD, adsorption of N. at 77 K. i.r. spectroscopy with adsorbed pyridine, Si and Al MAS-NMR and XPS. Bifunctional catalysts were obtained by impregnation with 0.3 wt% Pt, and the catalytic activity for the isomerization of a simulated LSR feed (n-Cj/n-Cj, 60/40 wt%) was measured under different reaction conditions. 

The catalysts were prepared by consecutive impregnation with aqueous solutions of Ru(N0)(N03)3 and Mg(N03)2. The support was an activated carbon (commercial one provided by ICASA, Spain, Sbet = 960.7 m g ) purified by treatment with HCl solution, to remove inorganic compounds. For comparative purposes, a ruthenium catalyst supported on a Y-AI2O3 (Puralox condea, Sbet = 191.9 m -g ) was also prepared by similar procedure. The impregnants were dried at 383 K and subsequently reduced. Before reaction and chemisorption measurements, samples were in situ reduced at 673 K for 2 h. Activity, selectivity and stability under reaction conditions were measured at atmospheric pressure in a fixed-bed quartz reactor kept at 823 K by cofeeding CH, CO2 and He as diluent. An equimolecular mixture of CH4 and CO2 (10% CH4, 10% CO2 and balance He) was adjusted by mass flow controllers (Brooks) and passed through the catalyst at a flow rate of 100 cm -min (space velocity = 1.2-10 h ). The effluents of the reactor were analysed by an on-line gas chromatograph with a thermal conductivity detector. 

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