Supported calcination

PtCU- helps to disperse the platinum evenly overthe support, while the adsorbed chlorine enhances the acidity of the support. Calcination and reduction produce the eventual catalyst. 

No determination was made as to whether differences between C0/AI2O3 and C0/K-AI2O3 were due to the presence of K, the higher support calcination temperature, or the lower surface area of K-AI2O3. It should be noted that although the total amount of bulk cobalt reducible in H2 at 480°C had increased in... 

Pt-Sn-Alumina Structure. No single model will adequately describe the above catalyst characterization data and the published data that has not been included because of space limitations. The relative distribution of both the Pt and Sn species depend upon a number of factors such as surface area of the support, calcination and/or reduction temperature, Sn/Pt ratio, etc. Furthermore, it appears that the "co-impregnated" and "co-precipitated" catalysts are so different that their structure should be considered separately. 

In the first series of experiments alumina support was formed with nitric acid as peptising agent. The support samples were calcined at three different temperatures (550, 750, and 800 °C, DN-650, DN-750 and DN-800). These alumina samples were submitted to the hydrothermal treatment (in water steam media) also at three different temperatures (150, 200 and 225 °C, Table 1 and Figs. 2 and 3). The results presented in Fig 2. clearly indicate that the alumina support calcined at 550 "C is not resistant against hydrothermal treatment in the applied temperature range. 

Similar dependencies were found for alumina supports calcined at 750 and 800 C (Table 1). For instance hydrothermal treatment of DN 750 sample (calcined at 750 °C) at 150 and 200 °C gave supports with surface area 142.5 and 41.4 m /g, respectively. 

However impregnation of DN 750 support with TEOS prevents from transformation of support structure and specific surface area and average pore radius after hydrothermal treatment was almost unchanged. Exactly the same results were obtained for supports calcined at 800 C. However the rate of decreasing in specific surface area and pore volume in the case of supports calcined at higher temperatures was found to be little lower than in the case of supports calcined at 550 °C. 

SI = Sibunit (activated pyrolytic carbon), A = Anthralur (active carbon). Subscript ox means oxidized support (with the oxidant indicated in the brackets) HT the support calcined in inert atmosphere at 1000 °C. Determined from Na2C03, NaOH, NaOEt, and HCl consumption in accordance with Boehm s method. Source Ref. 16. 

Taking into account the results with the powdered samples, monolithic supports were manu ctured, with CeOi contents between 0-4 wt%. The sihcate binders were necessary for the conformation of these structures [17]. The axial profile and mapping obtained by EPMA-WDS microscopy revealed that Ti and Ce concentration deviation over the wall cross-section were parallel and contrary to Si and Mg, principal components of the binders. This result indicated that cerium was selectively deposited on titania particles and not on the silicates. The Ce02 content added to titania and confirmed with ICP spectroscopy, total pore voliune and BET area for the three monolithic supports, calcined at 500 C for 4 hours are collated in Table 2. 

Butanediol conversion has been performed on Co-Zn/porcelain catalysts and supports alone. The effect of the support calcination and the pretreating with hydrochloric acid has been established. The possible reaction steps and intermediates have been defined by the quantum-chemical calculations. 

It has been established that 2,3-DHF was hydrogenated to THF under the similar reaction conditions [2]. To decrease the consecutive conversion of the reaction products and 1,4-BD intermolecular condensation to the polycondensation products the influence of the support calcination temperatiire on catalyst activity was examined during the simultaneous gradual 1,4-BD charging and products distillation away. The reaction results are summarized in Table 1. 

Influence of the support calcination temperature on 1,4-butanediol conversion in the presence of Co-Zn/porcelain catalysts ... 

As shown in Table 1 the activity of the catalyst depends on the support calcination temperature. The highest selectivity of 2,3-DHF was reached in the case of support calcined at 800-950 C but of the tetrahydrofuranoxy derivative - at 950 C. These supports and the catalysts on them have the largest surface areas 60-74 and 100-110 m /g, respectively. 

Support calcination temperature, °C Surface area, m /g THF yield. % Catalytic activity, mmol THF gcat h-1 Conversion, %... 

As seen (Fig. 2) the metal (Co, Zn)-phase is much better spread over the support surface in the inactive catalyst 5. The (Co+Zn) Si ratio characterizing the covering of the support is 1.25 in the sample 3 and 1.64 in the sample 5. This effect proves that the deposit of the active component covers and eliminates the catalytic active centres at the bare smface of the support. Thus, the support calcination at temperature higher than 950 °C leads to the decrease of the surface area and content of Si02 on the surface due to the interphase difhision and consequently to the decrease of SiOj accessibihty to a reactant. 

Many commercial experiments have been carried out over the years with many different types catalyst supports, calcined at various temperatures [407]. The concentration of chromium has been varied from as little as 0.01 wt% to as much as 6.0 wt% Cr. Higher chromium loading tends to increase the elasticity of the molten polymer. Many of the seemingly contradictory responses observed in Tables 23 and 24 as a result of changing the activation temperature were also exhibited when the chromium coverage was raised The breadth of the MW distribution remained constant whereas the rheological breadth increased. The low shear melt viscosity went up without an accompanying increase in MW. An Arnett... 

FIGURE 122 Melt indices of polymers made with silica-titania catalyst activated by the two-step process. Higher Ml values were obtained when the support was calcined in CO or CS2 rather than in air. (Support calcined in the gas shown at 871 °C, then impregnated with dicumenechromium(O) in hexane, followed by air at the temperature shown, and testing at 107 °C.)... 

Although there are many differences between chromium oxide catalysts and the organochromium catalysts, when they are bonded to the support, organochromium catalysts usually display a similar, but exaggerated, MW response in the polymer produced relative to what is observed with chromium oxide catalysts. For example, the MW of polymer produced with each type of catalyst usually decreased as the support calcination temperature was raised. Similarly, when both chromium oxide and the organochromium compounds were deposited onto aluminophosphate supports, they always yielded lower-MW polymer as the amount of phosphate in the support was raised. 

TABLE 55 Fraction of Product that was Liquid from Polymerization Tests Using Cr(DMPD)2 Deposited on Supports Calcined at Various Temperatures... 

Table 4 The effect of support calcination temperature and catalyst metal loading on the initial reaction rate and the selectivity to citronellol over Ni/silica fibers.

IR spectra of the supports were measured after drying in N2. The spectrum of pure alumina support, calcined at 400 °C, displays peaks at 3715 and 3680 cm and shoulders at 3760 and 3590 cm These are typical OH group peaks. The spectrum also shows adsorption at ca. 1550 and 1350 cm The spectrum for support calcined at 600 °C is similar but the OH region is more defined. 

AlaOs-supported (calcined) Re catalysts prepared from Re(acac)3 have a higher activity for the metathesis of hex-l-ene than catalysts prepared from NH4Re04, both alone and when promoted by various cocatalysts (BClimov 1993). 

Microwave heating has been reported to produce materials with particular physical and chemical properties [4], Stable solid structures are formed at low reaction temperatures with unusually high surface areas, making them very useful as catalysts or catalyst supports. Calcination of solid precursors in a microwave field has significant advantages over conventional heating. The effective synthesis of the catalysts and supporting adsorbents has been reported for the examples below. 

---