Palladium monoliths

In addition, Suzuki couplings were also investigated. For these examples the anion-exchange moiety of the palladium monolith 20 was converted to the hydroxide form 30 by washing with a sodium hydroxide solution. A solution of boronic acid and aryl halide was recirculated through the column furnishing the desired coupled... 

Figure 107. Conversion of (a) gaseous hydrocarbons (b) total particulate (PT) matter and (c) the soluble organic fraction (SOF) as a function of the exhaust gas temperature, reached over diesel eatalysts based on platinum or on palladium (monolith catalyst with 62 cells cm dedicated diesel washeoat formulations with platinum and palladium both at a loading of 0.35 g 1" and 1.41 g 1" in the fresh state heavy duty diesel engine bench light-off test at an average engine speed setting and various engine load settings).

Starting with a ceramic and depositing an aluminum oxide coating. The aluminum oxide makes the ceramic, which is fairly smooth, have a number of bumps. On those bumps a noble metal catalyst, such as platinum, palladium, or rubidium, is deposited. The active site, wherever the noble metal is deposited, is where the conversion will actually take place. An alternate to the ceramic substrate is a metallic substrate. In this process, the aluminum oxide is deposited on the metallic substrate to give the wavy contour. The precious metal is then deposited onto the aluminum oxide. Both forms of catalyst are called monoliths. 

Since 1981, three-way catalytic systems have been standard in new cars sold in North America.6,280 These systems consist of platinum, palladium, and rhodium catalysts dispersed on an activated alumina layer ( wash-coat ) on a ceramic honeycomb monolith the Pt and Pd serve primarily to catalyze oxidation of the CO and hydrocarbons, and the Rh to catalyze reduction of the NO. These converters operate with a near-stoichiometric air-fuel mix at 400-600 °C higher temperatures may cause the Rh to react with the washcoat. In some designs, the catalyst bed is electrically heated at start-up to avoid the problem of temporarily excessive CO emissions from a cold catalyst. Zeolite-type catalysts containing bound metal atoms or ions (e.g., Cu/ZSM-5) have been proposed as alternatives to systems based on precious metals. 

Catalytic materials can be physically supported on either pelleted or monolithic substrates. In the case of the pelleted catalyst, the support is an activated alumina. A typical monolithic catalyst is composed of a channeled ceramic (cordierilc) support having, for example. 300 to 400 square channels per square inch on which an activated alumina layer is applied. The active agents (platinum, palladium, rhodium, etc.) arc then highly dispersed on the alumina. 

Tonkovich et al. [123] claimed a 90% size reduction due to the introduction of micro channel systems into their device, which made use of the hydrogen off-gas of the fuel cell anode burnt in monoliths at palladium catalyst to deliver the energy for the fuel evaporation. A metallic nickel foam 0.63 cm high was etched and impregnated with palladium to act as a reactor for the anode effluent It was attached to a micro structured device consisting of liquid feed supply channels and outlet channels for the vapor, the latter flowing counter-flow to the anode effluent... 

A system for the Heck reaction between methyl acrylate and iodobenzene has been developed comprising an imidazolium-functionalized polystyrene monolith, initially for use in batch. This system could be reused six times before any reduction in yield was observed. Accordingly, a continuous-flow reactor system was developed using DMF at 200 °C with a residence time of 3-4 min to achieve full conversion. This system was characterized by very low palladium loadings (0.02 mol%), and ICP-MS of the solution aliquots showed leaching of less than 1 ppm. Attempts at using EtOH as solvent to provide a more environmentally and procedurally benign protocol resulted in maximum yields of 85% [144]. 

FIGURE 35 SEM image (A) and elemental maps of Al (B) and Pd (C) for a standard silica-coated cordierite monolith impregnated with palladium (705). 

FIGURE 38 Palladium distribution in the optimized monolith (A) cross section of channels, (B) enlarged view of center, (C) Si mapping, (D) Pd mapping. The thin silica layer and the palladium associated with it are clearly visible. Color bar indicates the Pd concentration. 

FIGURE 41 Elemental mapping of palladium at an intersection of the walls of a silica-coated acicular monolith. 

The market for gas cleaning is dominated by applications in automobiles and power plants, but it is interesting that in many more fields monoliths are applied, mainly because of their low-pressure drops. Emission control by monoliths is performed in several industrial plants, for example, phthalic anhydride plants (Siidchemie Envicat). A good example in the transport sector is the abatement of ozone that is present in the air fed to the cabins of airplanes. Palladium on ceramic monoliths appears to function well (142). 

H.A. Smits, Selective hydrogenation of model compounds for pyrolysis gasoline over a monolithic palladium catalyst, SPE thesis. Delft University of Technology, Delft, The Netherlands, 1994. 

H.A. Smits, A. Cybulski, J.A. Moulijn, W.Ch. Glasz, and A. Stankiewicz, Selective hydrogenation of styrene/l-octcnc mixtures over a monolithic palladium catalyst. Proceedings of the EUROPACAT-II, S7, 02, p. 515, Maastricht, Belgium, September 3-8, 1995. 

C. Reactors with Monolithic Palladium-Based Membranes... 

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