Silica reactor tube

Cells used for high-temperature measurements in furnaces often consist of silica sample tubes, supported by thin vanadium sleeves. The key to the analysis is whether it is possible to have a container that scatters in a sufficiently predictable way, so that its background contribution can be subtracted. With the current neutron flux available from both pulsed and reactor sources, sample volumes of... 

Specimens were placed in a silica reactor that was equipped with two side tubes for XPS and ESR measurements and connected to a circulation apparatus, described elsewhere [25, 26]. The catalysts, dried at 383 K, were characterized as prepared (a.p.), after heating in dry oxygen at 773 K (s.o.), or after reduction with CO. In some experiments, as specified, samples were exposed to NO, NH3, or various mixtures NO-O2-NH3. Electrons per V atom (e/V) were determined from the CO consumed. The average oxidation number of vanadium was calculated as 5 - eA/. 

The annular space between the reactor tube and shell contained the thermopiles and was thermally insulated with Santocell-powdered silica gel. 

The Pt/ZrO2 and Ce-promoted catalysts were prepared as described by Stagg and Resasco. All catalysts were reduced at 500°C for one hour before the reaction. The dry reforming reaction was performed in a fixed bed reactor. The reactor was a 0.3-m long ceramic reactor tube (6.35-mm o.d., 4.0-mm i.d.), sealed inside a stainless steel tube at higher pressures and contained a quartz thermocouple well. The reactor was loaded with 0.012 grams of catalyst mixed with 0.030 grams silica and held in place by quartz wool. The reactions were carried out at 800°C, and at 1 and 14 bar. Reaction products were monitored by a quadrupole mass spectrometer. 

Figure 13.11 Schematic of an hydride reactor used for particular elements. This automatic sampling device houses a mixing tube where the hydride of the metal (or non-metal) is formed during reaction with sodium horohydride. An argon flow extracts the metal hydride formed (gas separator) carrying it to a silica glass tube heated to between 800 and 1000 °C in the flame.

Redox experiments and ESR determination of Cu2+ were performed with a circulation all-glass apparatus equipped with a magnetically driven pump. The sample (0.2 to 1.0 g) was placed in a silica reactor equipped with a side ESR tube. All the samples before the redox cycles were treated in O2 at 773 K. The redox cycles consisted of (i) heating in He flow at 823 K for 2h, followed by evacuation at 773 K and heating in O2 at 773 K (ii) evacuation at RT followed by reduction with CO at 773 K (iii) evacuation at 773 K followed by a second treatment with O2 at 773 K. During the treatments (i) to (iii), the pressure of O2 or CO was monitored with a pressure transducer (MKS Baratron, sensitivity 1 Pa) until a nearly constant pressure was reached. All these measurements allowed the variation of the average oxidation number of copper to be followed. The acquisition or loss of electrons are expressed as e/Cu (number of electrons/total number of Cu atoms). At the end of treatments (i) to (iii), ESR spectra of Cu2+ species were recorded at RT. ESR measurements were carried out on a Varian E-9 spectrometer equipped with an on line computer. Absolute concentrations of... 

A, maintained at —170 to —196°C in order to freeze out the HF. From there it flows to the reactor furnace. The product gases flow through two silica U tubes or gas traps (I and I. The temperatures of I and II are —78°C and —196°C, respectively. Terminal trap B (maintained at —196°C), serves to prevent access of atmospheric moisture. 

I. Pure Hg is subjected to an additional purification over silica gel and is then slowly passed through a water-filled flask to saturate it with water vapor. The flask is held in an 85 °C thermostat. To avoid condensation of the water vapor thus taken up, the tube which connects the flask to the reactor is wrapped with electric heating tape and heated to about 100 °C. The Hg/HgO mixture then flows over a boat with WOg set in a porcelain or a quartz reactor tube surrounded a tubular electric furnace and heated to 800-900°C. The reduction is complete in 2 hours. The product is allowed to cool in an Og-free nitrogen stream. The nitrogen is admitted through a 3-way stopcock located between the water flask and the reactor. 

Silica and silica-supported oxide catalysts exhibit greater functionality in the partial oxidation of methane [108,109]. Siliea itself has measurable activity for CH4 conversion to HCHO, although at lower levels of activity than most other catalysts. Kasztelan and Moffat [110] have shown that up to 4.5% of CH4 co-fed with O2 can be converted at 866 K at a relatively high contaet time and with low selectivity (8%). Kas tanas et al. [ 111 ] noted that the Vycor or quartz walls of the reactor tubing had discernable activity for HCHO formation. Coupled products (mainly C2H6)... 

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