Calcining profile

By-products of these reactions are reclaimed and recycled. The color depends on the size of the particles formed. Size is controlled by regulating the calcination profile, ie, time and temperature. The calcined product is ground, washed, and classified. 

Figure 1, Simplified calcination profile. Reproduced with permission from reference 8b, Copyright 1981 Pergamon Press, Inc.

The hydration rate of sodium tripolyphosphate to its stable hexahydrate, Na P O Q 6H20, directly affects detergent processing and product properties. The proportion of STP-I (fast-hydrating form) and STP-II (slow-hydrating form) in commercial sodium tripolyphosphate is controUed by the time—temperature profile during calcination. In most processes, a final product temperature of near 450°C results in a product containing about 30%... 

Figure 2 shows the TPR profiles of the calcined phosphate precursors of the Ni2P/Si02, Ni2P/Al203, and NiaP/C-ALOj catalysts. 

Prior to inclusion of PVP-protected Pt nanoparticles the SBA-15 silica is calcined at 823K for 12h to remove residual templating polymer. Removal of PVP is required for catalyst activation. Due to the decomposition profile of PVP (Figure 6), temperatures > 623 K were chosen for ex situ calcination of Pt/SBA-15 catalysts. Ex-situ refers to calcination of 300-500 mg of catalyst in a tube furnace in pure oxygen for 12-24 h at temperatures ranging from 623 to 723 K (particle size dependent) [13]. Catalysts were activated in He for 1 h and reduced at 673 K in H2 for 1 h. After removal, the particle size was determined by chemisorption. Table 2 is a summary of chemisorption data for Cl catalysts as well as nanoparticle encapsulation (NE) catalysts (see description of these samples in proceeding section). 

FIGURE 6.3 TPR profiles of calcined (thick line) and reduced (thin line) catalysts (a) Co(20)/CyDTA/SiO2, (b) Co(5)/CyDTA/Si02, (c) Co(20)/SiO2, and (d) Co(5)/Si02. Heating rate 5 Kmin-1. 

Temperature-programmed reduction (TPR) profiles of fresh catalyst samples were obtained using a Zeton Altamira AMI-200 unit. Calcined fresh samples were first heated and purged in flowing argon to remove traces of water. TPR was performed using 30 cc/min 10% H2/Ar mixture referenced to argon. The ramp was 5°C/min from 50 to 1,100°C, and the sample was held at 1,100°C for 30 min. 

FIGURE 8.3 Temperature-programmed reduction profiles of (top) 25% Co/Si02 and (bottom) 15% Co/Si02, including catalysts calcined using (bold) 5% NO in N2 and (light)... 

Turning to the XANES results (Figure 8.4), upon reduction at 350°C, the extent of reduction is found to be higher for the H2-activated air calcined catalysts. This is evident in the shoulder at the edge (-7,709 eV), which is a measure of metallic content, as well as the lower white line intensity for the activated air calcined catalyst at -7,725 eV. The catalysts appear to contain a combination of mainly Co metal and CoO, in agreement with the interpretation of TPR profiles previously discussed. 

The presence of two peaks in the TPR profile for the Co/Ti02 system suggested that two cobalt oxide species were present on the calcined catalyst. Using XPS, these species were identified as C03O4 and Co+. The Co V /2 xpS spectrum of the calcined Co/Ti02 catalyst had a satellite peak due to a Co+ ... 

The Ni 2p2/o spectra from 2% Ni-loaded sepiolite (calcined at 850°C) after Pr/ atment is shown in Figure 6 along with the synthesized cur e profile and fitted Ni peaks located at 856.8, 854.6, and 852.2 eV. The positions for these Ni peaks are in agreement with those expected from compounds such as NiSiO-, NiO and Ni metal, respectively. Heating at 400°C in hydrogen did not reduce... 

Fig. 2. Time—temperature profile for kettle calcination. Points A—B represent the fill period B—C, the boil or drag C—D, falling rate or cook-off D, discharge for hemihydrate. Points D—E show firing rate to second boil E—F, second boil F—G, second cook-off G, second-settle discharge.

The zinc salt and BaS solutions are mixed thoroughly under controlled conditions (vessel geometry, temperature, pH, salt concentration, and stirring speed, see (a) in Fig. 20). The precipitated raw lithopone does not possess pigment properties. It is filtered off (b2) and dried (c) ca. 2 cm lumps of the material are calcined in a rotary kiln (d) directly heated with natural gas at 650-700 °C. Crystal growth is controlled by adding 1-2 wt% NaCl, 2 wt % Na2S04 and traces of Mg2 + (ca. 2000 ppm), and K+ (ca. 100-200 ppm). The temperature profile and residence time in the kiln are controlled to obtain ZnS with an optimum particle size of ca. 300 nm. 

Figurel shows the XRD patterns of sample A and sample B. Four distinct XRD peaks can be observed for sample A and sample B, except the ill-defined [210] peak of uncalcined sample B. The clear four-peak profiles appearing at low angles show the presence of long-range order mesopores for samples A and B. The structural data show that, upon calcination at 550 °C, the d spacings were contracted due to the removal of surfactant from mesopores.

Figure 3. TPR profiles of (A) CoAI-LDH and (B) CoAISn-LDH calcined at different temperatures for 5h (a) Uncalcined, (b) 300, (c) 450, (d) 700, (e) 900, (f) 1100 °C The inset in Figure 3 A shows the variation of the position of TPR first peak with respect to the calcination temperature...

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