Laser activated pyrolysis

In this section preparation and characterization of catalytic materials are briefly reviewed with respect to their applications in environmental catalysis. A number of techniques for the preparation of the supports and catalysts are emphasized. Techniques such as impregnation, homogeneous deposition precipitation, grafting, hydrolysis, sol-gel, and laser-activated pyrolysis are used for the preparation of catalysts for fundamental studies. 

Laser-activated pyrolysis has been applied for the synthesis of ultrafine Ti02 with titanium isopropoxide or ethoxide as precursors [33]. A specific surface area of 128m g was obtained. 

Titania-supported vanadia catalysts have been widely used in the selective catalytic reduction (SCR) of nitric oxide by ammonia (1, 2). In an attempt to improve the catalytic performance, many researchers in recent years have used different preparation methods to examine the structure-activity relationship in this system. For example, Ozkan et al (3) used different temperature-programmed methods to obtain vanadia particles exposing different crystal planes to study the effect of crystal morphology. Nickl et al (4) deposited vanadia on titania by the vapor deposition of vanadyl alkoxide instead of the conventional impregnation technique. Other workers have focused on the synthesis of titania by alternative methods in attempts to increase the surface area or improve its porosity. Ciambelli et al (5) used laser-activated pyrolysis to produce non-porous titania powders in the anatase phase with high specific surface area and uniform particle size. Solar et al have stabilized titania by depositing it onto silica (6). In fact, the new SCR catalyst developed by W. R. Grace Co.-Conn., SYNOX , is based on a titania/silica support (7). 

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

Our data can be used to estimate the effective temperatures reached in each site through comparative rate thermometry, a technique developed for similar use in shock tube chemistry (32). Using the sonochemical kinetic data in combination with the activation parameters recently determined by high temperature gas phase laser pyrolysis (33), the effective temperature of each site can then be calculated (8),(34) the gas phase reaction zone effective temperature is 5200 650°K, and the liquid phase effective temperature is 1900°K. Using a simple thermal conduction model, the liquid reaction zone is estimated to be 200 nm thick and to have a lifetime of less than 2 usee, as shown in Figure 3. 

The catalytic activity for Fischer-Tropsch synthesis of the Fe-carbides (Fe2C and Fe7C3) produced by laser pyrolysis has been evaluated and compared to that of a precipitated iron oxide catalyst. Details of the results of these studies are the subject of chapter 19 of this book.35... 

It was found that an iron carbide catalyst produced by laser pyrolysis and a commercially available ultrafine iron oxide catalyst are not as active for FTS as a precipitated iron catalyst. Operating under industrial conditions, it was found that the unpromoted precipitated catalyst had a hydrocarbon productivity 93% of that reported by Kolbel while the novel catalysts were far below Kolbel s benchmark. It was found, however, that at similar CO conversion, the iron carbide catalyst had a higher hydrocarbon production rate and had a better selectivity for C5+ hydrocarbons. 

Exposure to synthesis conditions caused all three catalysts to oxidize to Fe304. It is interesting that even though each catalyst ultimately transformed to Fe304, they each had different activity and selectivity. This implies that the active phase is on the surface of the. catalyst and not in the bulk. The catalyst prepared by laser pyrolysis appeared by XRD to be a... 

The limited knowledge of thermal behaviour of halogenated acids has been extended significantly by a pyrolysis (infrared laser-powered) and semiempirical study which has established that mono-, di- and tri-chloroacetic, trifluoroacetic, and bromoacetic acid eliminate HX and that both bromo- and iodo-acetic acid undergo C—X bond homolysis acetic acid undergoes decarboxylation and dehydration under the same conditions.46 The semiempirical calculations of corresponding activation energies are consistent with these conclusions. 

Molecules may be subjected to various stresses before they are ionized. Examples include pyrolysis, rf or mw heating, electron attachment, laser irradiation, collisions with radicals or other highly reactive species, etc. The unstable products and transients, which may also be highly excited, often constitute the sample introduced into the photoelectron spectrometer. The investigation of these transients, which may be referred to as active electron spectroscopy has provided much information about the existence, formation and properties of many previously unknown neutral, ionic and radical species. 

In general, several possible chemical reactions can occur in a CVD process, some of which are thermal decomposition (or pyrolysis), reduction, hydrolysis, oxidation, carburization, nitridization and polymerization. All of these can be activated by numerous methods such as thermal, plasma assisted, laser, photoassisted, rapid thermal processing assisted, and focussed ion or electron beams. Correspondingly, the CVD processes are termed, thermal CVD, plasma assisted CVD, laser CVD and so on. Among these, thermal and plasma assisted CVD techniques are widely used, although polymer CVD by other techniques has been reported. ... 

Two different methods, based on flame and laser pretreatments, were investigated. These methods are generally applicable under atmospheric conditions. The first is based on the surface reaction of low-molecular, silane-based precursors which are activated by pyrolysis in a propane gas flame. XPS analysis of the pretreated surface shows a thin silicate layer on the surface which remains active for about 10 days. After a careful parameter optimization, adhesion strength can be greatly improved, especially on steel surfaces. A similar method is commercially available as the Silicoater process. The second method, CLP, is based on a laser pretreatment in combination with a specific primer [4]. With parameters optimized for the specific substrate, adhesion strength can be greatly improved, especially on aluminum surfaces. 

The preparation of nanomaterials is one of the most active fields in material science. Number of techniques have been used for the production of nanoparticles gas-evaporation [11], sputtering [12], sol-gel method [13], hydrothermal [14], microemulsion [15, 16], polyols [17], laser pyrolysis [18], sonochemical synthesis [19], chemical coprecipitation [20-22], and so on. Among them, the surfactant assembly mediated synthesis is attracting more attention because it allows for a good... 

Figure 3 Third dimension in pyrolysis mass spectrometry approaches (A) linear programmed thermal degradation mass spectrometry [LPTDMS - third dimension = temperature] (B) collisionally activated dissociation of parent ions coupled with scanning of product ions using tandem mass spectrometry [MS/ MS - third dimension = spectrum of product ions] (C) laser microprobe mass analyser [LAMMA - third dimension = spatial resolution].

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