Catalytic laser effects

In the near future, the possible synthesis of nanotubes with solid-gas potential will be more favorable to adsorption. The effect of hydrogen overpressure on the stability of adsorbed Ha needs to be verified in the near future. The high-purity nanotube produced by laser vaporization, catalytic decomposition, or other techniques should be investigated. It is noteworthy that the synthesis of the SWNT with defined diameters and distances between the walls is difficult to perform at present, but future synthesis routes will allow more... 

The titanosilicate version of UTD-1 has been shown to be an effective catalyst for the oxidation of alkanes, alkenes, and alcohols (77-79) by using peroxides as the oxidant. The large pores of Ti-UTD-1 readily accommodate large molecules such as 2,6-di-ferf-butylphenol (2,6-DTBP). The bulky 2,6-DTBP substrate can be converted to the corresponding quinone with activity and selectivity comparable to the mesoporous catalysts Ti-MCM-41 and Ti-HMS (80), where HMS = hexagonal mesoporous silica. Both Ti-UTD-1 and UTD-1 have also been prepared as oriented thin films via a laser ablation technique (81-85). Continuous UTD-1 membranes with the channels oriented normal to the substrate surface have been employed in a catalytic oxidation-separation process (82). At room temperature, a cyclohexene-ferf-butylhydroperoxide was passed through the membrane and epoxidation products were trapped on the down stream side. The UTD-1 membranes supported on metal frits have also been evaluated for the separation of linear paraffins and aromatics (83). In a model separation of n-hexane and toluene, enhanced permeation of the linear alkane was observed. Oriented UTD-1 films have also been evenly coated on small 3D objects such as glass and metal beads (84, 85). 

Recent discussions of stratospheric chemistry have dealt with the effect of freons on ozone balance through a Cl/ClO catalytic destruction of ozone. The fundamental absorption band of CIO is measured to be at 11 /xm. Isotopically substituted CO2 laser based OA absorption measurement technique should allow us to carry out fundamental measurements on CIO and its diurnal variation in the stratosphere to provide yet another important parameter (in addition to NO above) in the stratospheric ozone chemistry. 

This section describes a simple model that enables evaluation of the influence of charge effects on the catalytic activity of metallic nanostructures. Also, the results of experiments performed with nanostructured catalysts synthesized by laser electrodispersion are discussed. These results demonstrate a relationship between the catalytic activity and charge density in the... 

There are many reasons why mass spectrometry misses the high masses. One of these is that the detectors measure in a linear mass mode which soon loses small numbers of molecules in the background noise, contrast this with SEC which collects logarithmically with mass. The detectors are often mass sensitive and this can be corrected to some extent by applying a data manipulation function. Other factors which need to be taken into consideration are loss of low mass regions due to either volatility or ionization problems. This is particularly apparent when looking at condensation polymers or acrylics from catalytic chain transfer polymerization. There are also effects on the mass distribution due to the laser power used thus the minimum laser power is often required but not always applied. 

The temperature of zeolite samples containing various adsorbed molecules was switched from room temperature to 500-600 K within 30-40 seconds by means of a laser beam. Catalytic n-alkane cracking and H-D exchange with deuterated cyclohexane were monitored by IH MAS NMR in time steps of down to one second. A two-dimensional representation of the chemical shift and the chemical reaction of the species will be given, allowing a good characterization of reaction steps. At low temperature a weak proton transfer without chemical reaction can be observed, whereas at 430 K and 530 K the proton transfer is accompanied, respectively, by an isomerization or a decomposition to methane and coke. In addition to the effect of high temperature, the laser radiation itself can force the conversion of alkanes to methane and coke. 

Wave mixing of two electric fields can give rise to second-order effects of nonlinear optics [4]. One of these is the harmonic generation that converts the fundamental wavelength of a laser into its half (see Section 12.2.2). But, if electric fields at different frequencies are used, the response of a medium with sufficient second-order dielectric susceptibility can be frequency shifted to the sum and the difference of the two laser frequencies [4]. In particular, sum frequency generation (SFG) is often used to study surfaces and has found applications to examine catalytic combustion [9,36]... 

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). 

Many chemical reactions can be enhanced by catalytic effects at solid surfaces. The prospect of increasing these catalytic enhancements further by laser irradiation of the surface has initiated intense research activity [1395, 1396]. The laser may either excite atoms or molecules adsorbed at the surface, or it may excite desorbed molecules just above the surface. In both cases the desorption or adsorption process is altered because excited molecules have a different interaction potential between the molecule M and the surface than the ground-state molecules. Furthermore, the laser may evaporate surface material, which can react with the molecules. 

Many chemical reactions can be enhanced by catalytic effects at solid surfaces. The prospect of increasing these catalytic enhancements further by laser... 

---