Uncalcined catalysts

ESCA Sample Pretreatment. Samples were pelleted and cut to fit into a rectangular depression in an ESCA sample probe similar in design to one used by Hercules (16). The portion of the probe holding the catalyst sample could be withdrawn into an outer cylinder and sealed under an atmosphere of the pretreatment gas. For pretreatment the calcined samples were exposed to a hydrogen flow at one atmosphere and heated to AOO C. After this pretreatment the sanqile was withdrawn into the insertion tube, sealed in the pretreatment gas, inserted into the ESCA, evacuated, and then the ESCA spectra were recorded. A similar procedure was followed for the uncalcined catalysts except that the temperature was first increased in hydrogen flow to SOO C and held at this temperature for 3 to 4 hours the sample was then heated to 400 C and held at this temperature for 18 hours. 

In the hydrated form the active site will permit exchange of 1H+ per aluminum by alkali ions functioning as a Bronsted acid. In the anhydrous form each mole of aluminum will represent a mole of Lewis acid. These suggestions are consistent with the observation that the sum of the Lewis and Bronsted acids in a given catalyst remain relatively constant over a range of temperatures and that the Bronsted acid present in an uncalcined catalyst equals the Lewis acid in the calcined catalyst 8). 

The BET isotherm plots for the Cr(VI)/Sn02 catalyst (Figure 4) show that tlie isotherm for uncalcined catalyst is typical for adsorption onto a microporous solid (type 1 isotherm). This form of isotherm is retained after calcination at 300°C, but after calcination at higher temperatures the isotherm changed drastically in form. Calcination at 1000°C resulted in an isothenn characteristic of a type III non-porous solid. Whilst after calcination at 600°C the material exhibited intermediate behaviour and was mesoporous. 

The relative amounts of the two components detnmine both the attrition resistance and the activity. Increasing the amount of uncalcined catalyst increases the activity but decreases the attrition resistance. AI, B, Zr and phosphoric acid act as binders in order to increase the attrition resistance. 

The uncalcined catalysts were characterized by FTIR and XPS measurements. 

As indicated in table 2, the absolute content of residual carbon (C(I)) on the uncalcined catalysts prepared from inorganic precursors is very low and comparable with the one observed on pure silica (C(I)/Si = 0.25). This precludes the traditionnal use of this signal as internal standard for the calibration of the binding energy scale in our silica-supported catalysts and justifies its replacement by the well-defined Si2p photopeak. 

Isopropyl alcohol can be oxidized by reaction of an a,P-unsaturated aldehyde or ketone at high temperature over metal oxide catalysts (28). In one Shell process for the manufacture of aHyl alcohol, a vapor mixture of isopropyl alcohol and acrolein, which contains two to three moles of alcohol per mole of aldehyde, is passed over a bed of uncalcined magnesium oxide [1309-48-4] and zinc oxide [1314-13-2] at 400°C. The process yields about 77% aHyl alcohol based on acrolein. 

The Re peak, present as a doublet in this catalyst, resembles the one obtained for Re20 on tape. This suggests, if rhenium hydroxides may be eliminated from consideration, that the calcined rhenium catalysts may have some rhenium in a valence state lower than 4-7. However, even reduction at 400 C of the uncalcined Pt-Re sample does not produce an observable amount of Re(0). 

Both uncalcined and calcined LDHs have also been shown to be effective supports for noble metal catalysts [18-25]. For example, palladium supported on Cu/Mg/Al LDHs has been used in the liquid phase oxidation of limonene [24], and on calcined Mg/Al LDHs for the one-pot synthesis of 4-methyl-2-pentanone (methyl isobutyl ketone) from acetone and hydrogen at atmospheric pressure [25]. In the latter case, the performance depends on the interplay between the acid-base and hydrogenation properties. More recently. 

Diffused reflectance spectrum of the 7.9 % V205/AIP04-5 sample after calcination at 550°C was drastically different from that of the uncalcined sample (Fig. 6). The sample before calcination showed a broad charge-transfer band at 400-550 nm. However, the sample after calcination showed a charge-transfer band at 270 nm. In a previous study on surface phases of VjOg supported catalysts [23,24], ions in a distorted... 

Narayanan, S. and Krishna, K. (1998). Hydrotalcite-supported palladium catalysts Part I preparation, characterization of hydrotalcites and palladium on uncalcined hydrotalcites for CO chemisorption and phenol hydrogenation. Appl. Catal. A 174, 221. 

Before being used as a catalyst, the material was calcined in air at 750 C for 1.5 hours. After calcination, the color of the catalyst was bright vellow and a 257. weight loss was noted. BET surface areas of uncalcined and calcined materials were 20.7 and 8.7 m /g, respectively. 

Figure 5.20 Spikelet echo spectra of the central transition obtained for uncalcined and calcined MoO /AfOs catalysts with 16wt% and 24wt% loadings, (a) 16% uncalcined,...

Hodge NA, Kiely CJ, Whyman R, Siddiqui MRH, Hutchings GJ, Pankhurst QA, Wagner FE, Rajaram RR, Golunski SE (2002) Microstructural comparison of calcined and uncalcined gold/iron-oxide catalysts for low-temperature CO oxidation. Catal Today 72 133... 

The titanium content of the catalysts was determined by AES-ICP and the carbon content by total combustion in oxygen at 1050°C followed by an acidimetric coulometry measurement. DRIFT spectra of uncalcined samples were measured in inert nitrogen atmosphere conditions on a Nicolet Impact 400 D FTIR spectrometer within the spectral range of 4000 - 400 cm with a resolution of 2 cm and the number of scans equal to 64. 

FIGURE 134 Surface areas of Cr/silica catalysts, showing the promotion of sintering by the presence of fluoride. The fluoride coverage in F atoms nm 2 is based on the initial (uncalcined, unfluorided) surface area. 

The specific surface area (As ) of the uncalcined Cr(VI)/Sn02 catalyst (BET, 114 m g-l as, 125 m g-1) is considerably lower than that of tin(IV) oxide gel itself (185 m g-l). The specific surface area of the neat oxide decreases steadily with increase in temperature to a value of 40 m2 g-l after calcination at 1000°C. In contrast, that of the Cr(VI)/Sn02 catalyst decreases by ca. 15% to ca. 100 m2 g-l after calcination at 300°C, by ca. 50% to 58 m2 g-l after calcination at 600°C, and falls dramatically to nearly zero after calcination after calcination at 1000°C. 

Matsuchita et al. [38] have used RuCoAl hydrotalcites for highly efUcient oxidation of alcohols and aromatic compounds using molecular oxygen. Zhu et at. [39] studied hydroxylation of phenol in the liquid phase over copper containing (CuAI-HT) hydrotalcites. The results inferred that among the catalysts studied, the catalyst with Cu/AI 3 atomic ratio showed the highest activity for the conversion of phenol and activity of the fresh (uncalcined) samples was higher than the calcined samples. Ternary hydrotalcites such as Ni(Mg)Al, Mg(Mn)AI, have also been found active for various oxidative transformation reactions [40]. 

Catalyst inactivation can also be brought about by inorganic basic ions. The exchange of potassium ion onto an uncalcined synthetic silica-alumina causes loss of activity. The results (Mills, Boedeker, and Oblad, 21) are given in Table IV. That inactivation was not due to a... 

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