Catalytic Conversion and Enhancement

Automobiles emit pollution mostiy in the first 5 min after start-up because Pt- or Pd-based catalysts currently used in automobile exhaust cleanup are inactive below a temperature of 200 °C. The low-temperature gold catalysts are very inactive unless the gold is in the form of particles smaller than 8 nm in diameter. However, self-ignition of Pt nanoparticles happens at room temperature by exposing the particles to methanol/air or ethanol/air gas mixtures. Designing efficient catalysts working at low temperature for both oxidation and reduction is greatly desired for environment protection. 

The presence of defects opens new pathways which significantly decrease the thermal stability of the reconstructed Rh(llO) surfaces [39]. Although the activity of electrochemical oxidation of carbon monoxide and methanol electro-oxidation can be increased by increasing surface steps on Pt nanoparticles, the oxygen reduction reaction activity of the 2-nm-sized Pt nanoparticle has been found insensitive to the step area, as shown in Fig. 20.3 [40], in contrast to the methanol oxidation reaction activity. 

DFT calculation results in Fig. 20.5 show the polarization of the valence electrons of gold solid clusters and hollow cages and the activation energies for CO oxidation [49]. The lower the effective atomic CN is, the stronger the polarization and the lower the activation energy will be for CO oxidation of the gold catalyst, which is in accordance with observations for Pt catalysts shown in Fig. 20.3. Bond contraction, core electron entrapment, and valence charge polarization happen only to the outermost two atomic layers [49-51]. 

Therefore, a high degree of atomic undercoordination by size reduction or proper hetero-coordination by alloy or compound formation could be effective approaches for the efficient catalyst design because the broken-bond- and inter-face-bond-induced quantum trapping and polarization that determines the direction and extent of valence charge flow between the gaseous specimen and the catalyst. 

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Properties that bulk materials never show merge at the nanoscale such as conductor-insulator transition, dilute magnetism, Dirac-Fermi polarons, catalytic conversion and enhancement, superhydrophobicity, superfluidity, super lubricity, and supersolidity. 

Promoters function in several ways to increase the conversion/yield in catalytic processes and enhance the selectivity towards desired products and the stability of the catalysts. These improvements, often realised at few percentage levels, contribute significantly towards the process economics. Since the cost of the feedstocks constitute 70 % of the cost of products in hydrocarbon processing industry, processes with improved selectivity is the need of the day and it is here that promoters have a mojor role to play. ... 

In general, NO and NO2 are mutually beneficial for NOx reduction over the SCR catalysts tested. That is, the presence of NO enhances the NO2 conversion, and vice versa. This results in the synergistic effects of NO and NO2 in the catalytic reduction of NOx with NH3 over CuZSMS, FeZSMS and V20s/Ti02 catalysts. 

Battelle has developed an efficient process for the thermo-catalytic conversion of succinate into pyrrolidones, especially N-methyl-2-pyrrolidone. The process uses both novel Rh based catalysts and novel aqueous process conditions and results in high selectivities and yields of pyrrolidone compounds. The process also includes novel methodology for enhancing yields by recycling and converting non-useful side products of the catalysis into additional pyrrolidone. The process has been demonstrated in both batch and continuous reactors. Additionally, stability of the unique Rh-based catalyst has been demonstrated. 

Friedel-Crafts acylation is widely used for the production of aromatic ketones applied as intermediates in both fine chemicals and pharmaceutical industries. The reaction is carried out by using conventional homogenous catalysts, which represents significant technical and environmental problems. The present work reports the results obtained in the Friedel-Crafts acylation of aromatic substrates (anisole and 2-methoxynaphthalene) catalyzed by Beta zeolite obtained by crystallization of silanized seeds. This material exhibits hierarchical porosity and enhanced textural properties. For the anisole acylation, the catalytic activity over the conventional Beta zeolite is slightly higher than with the modified Beta material, probably due to the relatively small size of this substrate and the weaker acidity of the last sample. However, the opposite occurred in the acylation of a bulky substrate (2-methoxynaphthalene), with the modified Beta showing a higher conversion. This result is interpreted due to the presence of a hierarchical porosity in this material, which favors the accessibility to the active sites. 

Recently, cross-aldol condensation of benzaldehyde with n-heptaldehyde to give jasminaldehyde (Scheme 13) has been reported a mesoporous molecular sieve Al-MCM-41 with supported MgO was the catalyst. The reactions were carried out in a stirred autoclave reactor with a molar benzaldehyde/heptanal ratio of 10 at 373-448 K (236). The results show that Al-MCM-41 is catalytically active, and its activity is significantly increased by the deposition of MgO (Table V). Increasing the amount of deposited MgO on Al-MCM-41 decreases the surface area but enhances the catalyst basicity. The basicity is well correlated with the catalytic activity, although the selectivity to jasminaldehyde is not the selectivity is essentially independent of temperature, pressure, time of the reaction, and conversion. 

A new catalyst formulation containing alkali metals and W on a silica support gives more promising results.549 Alkali metals are able to lower the phase transition temperature from amorphous silica to a-crystoballite, shown to be critically important for an effective catalyst, while incorporation of W enhances catalytic activity to ensure high methane conversion and excellent ethylene selectivity. An alkali-stabilized tungsten oxo species is thought to be the active site. 

The oxidation of propane into acrylic acid in the presence of heteropoly catalysts prepared from H3PM012O40 and antimony pentachloride gave rather low conversion and selectivity [10 and 19%, respectively (2% yield)] (352). Recently, a yield of ca. 9% was obtained with H5PV2M010O40 (353). The addition of Cr ion also enhanced the catalytic performance (354). 

Copper(II) complex (5) catalyses the oxidation of sulfides to sulfoxides with hydrogen peroxide in high yields. Addition of a catalytic amount of TEMPO to the reaction mixture enhances the conversion and selectivity.181... 

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