Catalyst, content measurement

Pd-, Pt-, Al- and Si-content of catalysts was measured by ICP apparatus. The surface area was calculated by BET-plots and t-plots. Metal dispersion was determined from the amount of chemisorbed CO and acidity was determined from the chemisorbed NH3. 

After this exposure, the oxygen content of the catalyst was measured. 

A new reactor concept for the study of catalyst deactivation is presented, it consists of the combination of an electrobalance and a recycle reactor. With the electrobalance, the coke content on the catalyst is measured continuously. The recycle reactor operates gradientlessly at high conversion, with on-line gas chromatographic analysis of the effluent. Thus, the catalyst activity and product selectivities may be coupled directly with the coke content and the coking rate on the catalyst. 

In the electrobalance technique, the coke content on the catalyst is measured continuously. The combination with on-line gas chromatography couples the catalyst activity with its coke... 

The used catalysts were washed with toluene in a Soxhlet extractor, stored in purified toluene and dried before analysis. C, H, S and N elemental analysis were performed by combustion using a Carlo Erba apparatus. The coke content is therefore defined in this work as being the carbon content of a used catalyst washed by hot toluene. Metal contents were measured by X-ray fluorescence spectroscopy. The coke hydrogen content was determined by difference between the hydrogen content measured for the used catalyst and the hydrogen content measured for the fresh NiMo catalyst (0.6 wt %). 

To analyse the variation of catalytic activities of the used catalysts, carbon contents measured on the used samples removed after tests using model molecule have been used. As can be noted in Table 1, the cyclohexane isomerization activity at 380°C or at 400°C is not measurable compared to the activities of the fresh catalyst. This indicates that the isomerization sites are strongly poisoned by the deposits. It is dear in Table 1 that even the samples containing less than 200 ppm V are strongly poisoned indicating that the catalyst acidity has been considerably neutralized by the carbon deposit. 

Figure 2. Phenol and ether content vs. asphaltene content for liquid products made under a variety of conditions employing CoMo/Al203 catalyst Asphaltene contents taken from Ref. 21 phenol content measured by direct titration and ether content taken by difference...

Fig. 26. Comparison of acidity of NiP/Al, MoP/Al, and NiMoP/Al catalysts as measured by cyclopropane (CP) cracking as a function of P content [reprinted with permission from Iwamoto (67)].

Metal loadings were determined from uptake of the catalyst precursor. The Os content measured after 24 h on stream was 0.90%. 

Coronene adsorbs on catalyst sites present on both the alumina support and on the active NiMo sulfide phase 3). It has been found that adsorption decreases with coke content to a very Jow value at high coke levels (4), Therefore, it appears that coronene adsorption on the coke is nil. On this basis, it is assiimmed that the loss in adsorption with increasing coke is proportional to the loss in pore surface area due to coverage by coke. The results of coronene adsorption measurements on the VGO-coked catalysts show an initial drop for the 2% C sample, but little change thereafter for higher coked catalysts (Fig. lA) This implies that the coke Is concentrated near the mouth of the pores, On the other hand, catalyst dlffusivity measurements show a continual and sig-... 

The preparation of CoMo/AAP catalysts has been reported in ref, 5. The metal contents of the catalysts were determined by ICP-AKS-The specific surface areas of the catalysts were measured by the traditional BET method with nitrogen adsorption. The pore size distributions were measured by inecury penetration method,... 

On the samples aged under propane for 6 hours, the surface area losses ( S) of the catalysts were measured (table III], together with the carbon content. 

Differential Scanning Calorimetry. DSC scans for the M-B-23/25-48 series are shown in Figure 10. At low catalyst concentrations, there are two prominent endotherms at ca. 215°C and 225°C. As catalyst content increases, a new broad endotherm appears at ca. 190°C. These endotherms are characteristic of all polyol systems polymerized at high catalyst concentrations and/or high mold temperatures (Figure 11). Multiple endotherms in MDI/BDO polymers have been previously reported by other investigators (e.g. ref. 4, 14, 16, 17). Overall heats of fusion are a measure of crystallinity and crystal perfection and size and were higher (24 J/g) for samples with low catalyst content. 

When the coke content of the catalyst is measured a distinction can be made between the deactivation function for the main reaction, (p, and that for the coking reaction tpc defined by ... 

BET surface areas of the SOj deactivated catalysts were measured with a Micromeritics Accusorb 21(X)E using liquid Nj at 77 K after the catalysts had been pretreated in vacuo at 180°C for 10 h. Sulfur and carbon contents of the deactivated catalysts were determined by an oxidation method with a LECO SC-132 Sulfur Systems and CS-044 Carbon Sulfur 781-000 Systems (LECO Co.). 

Although the catalysts showed high initial activity, rapid deactivation was also observed. For example, when using a Pt/t -alumina catalyst at 250 C, essentially complete TCA conversion was observed initially however, after 15 h TCA conversion had declined to < 25 percent. To understand the deactivation process, surface acidity and basicity, coke content, chlorine content, and platinum content were measured for both the fresh and the used catalysts. These measurements showed that up to 40 wt% coke formed on the supported platinum catalyst and that the acidity changed significantly during the reaction at 350°C. 

Chemisorption uptakes of Hj at 298-303 K for alumina supported nickel catalysts were measured. The corresponding nickel surface areas were calculated and subsequently sulfur contents at saturation were determined. The average values were of the same magnitude as the amounts of sulfur that were not desorbed from the catalysts during the TPH treatments. Hence, it may be concluded that the saturation layer of sulfor remains on the catalyst even after regeneration in hydrogen atmosphere. 

The deactivated catalyst recovered from the reactor after each run was analysed for its coke content using a LECO CS244 carbon/sulphur analyzer. The total surface area of the fresh and spent catalysts were measured using a Quantasorb Sortometer in the Catalyst Characterization Laboratories at Kuwait Institute for Scientific Research. The catalyst pore structures were also examined through a scanning electron microscope and images of the fresh and spent catalyst. 

Nominal metallic content of monometallic catalysts was 1 and 0.5 wt% in ruthenium for adsorbed and impregnated catalyst respectively, while that of bimetallic catalysts was 0.5 -1-1 wt% for the coadsorbed, and 0.25 + 0.5 wt% for the coimpregnated, in Ru and Pt, respectively. The actual metal loading of the corresponding catalysts as measured by AAS are summarised in Table 1. 

The platinum contents of the prepared catalysts were measured by Atomic Absorption Spectroscopy using a Varian Spectra AA 400 phis. In preparation for analysis, all samples were dissolved in aqueous HF and only measured platinum loadings will be referred to below. 

FIGURE 5 Silanol group measurements of Cr/silica catalysts. The AOH/Cr ratio was determined from the OH group content measured with and without Cr03 applied. It is proportional to the original OH population, so that the fraction of OH groups displaced by any chromium loading is constant with calcination temperature. 

The coke content of the catalysts was measured by combustion-volumetry after the run. The differential thermal analysis (DTA) of the used catalysts was performed with an Aminco Thermoanalyzer using oxygen as dynamic gas. The soluble fraction of coke from used catalysts was extracted with solvents and the solutions were analyzed by several techniques in order to determine their nature. 

The Pt content in the Pt-MCM-41-IS, Pt-MCM-41-IE and R-MCM-41-IMP catalysts was determined by energy dispersive X-ray micro-analysis attached to SEM. The Pt content in the catalysts was measured as follows Pt-MCM-41-IE (0.1 wt %) < Pt-MCM-41-IMP (2 wt %) < R-MCM-41-IS (5 wt %) Table 1. The low loading of R in R-MCM-41-IE is attributed to the difficulty in introducing Pt to zeolites and mesoporous materials by ion-exchange method. Hence introducing of Pt via in-situ synthesis provides a better alternative for preparation of high loading of Pt modified MCM-41 catalyst. 

The iron content of the catalyst samples was determined by chemical analysis after dissolution of the zeolite in concentrated sulfuric acid. The I.R. characterization was carried out by using the KBr technique. The amount of nitrogen in the catalyst was measured by the standard chemical method. 

In order to substantiate this measure of chromia area, the rates of carbon monoxide oxidation over the various catalysts were measured. It was found that the alumina portion of the surface could be rendered inactive by selective poisoning with water and, under these conditions, the reaction was catalyzed exclusively by the ehromia surface. Since the activation energy was independent of the chromium content, it was reasonable to expect a linear variation of specific activity (i.e., activity per unit total surface area) with the fraction 0 (Table I) of the total surface contributed by the chromia phase. In Fig. 3 the specific rate is... 

From the slope of the plots of Fig. 6, the initial deactivation rate was calculated as do = [- da/dt ]h). In Fig. 7, the do values obtained for all the samples are represented in open squares as a fimction of the carbon content measured after the catalytic runs (Table 2) clearly, it does not exist any correlation between do and the amount of coke. Initial deactivation is lower on AI2O3 (do = 0.14 h" ) than on MgO (do = 0.53 h ) in spite that alumina forms more coke during reaction and that the coke is more difficult to oxidize as compared to MgO (Table 2 and Fig. 4). These results show that neither the coke amount nor its polymerization degree account for the catalyst deactivation order observed in Fig. 6. A better explanation is obtained by considering the nature of the surface sites that are responsible for the formation of coke precursors on pure AI2O3 or MgO. Alumina contains Brbnsted (OH groups) and Lewis (metal... 

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