Catalyst energy generation

When catalytic reaction rates become very large, it is possible that the energy generated (or consumed) by reaction cannot be dissipated (or supplied) at a rate that is sufficient to keep the entire catalyst pellet at the same temperature as the surrounding fluid. Temperature gradients... 

Figure 2 depicts a typical manufacturing facility. Inputs to the facility include raw materials to produce the saleable product(s), water, air, solvents, catalysts, energy, etc. Outputs from the facility are the saleable product(s), waste energy, and gaseous, liquid, water, and solid wastes. In contrast, a manufacturing facility with an absolute minimum (but not zero) amount of waste being generated is shown in Fig. 3. Inputs to the facility include only the raw...

Zirconia cells with Pt catalyst-electrodes can also be used to convert ammonia to nitric oxide with simultaneous electrical energy generation (6-7). Other industrially important oxidation reactions have been recently proposed for solid-state electro-... 

In asymmetric catalysis a prochiral substrate binds to an enantiomerically pure catalyst to generate a pair of diastereomeric intermediates. The energy difference and the rate of exchange between them controls the optical yield (e.e.) of the final product. In the case of a-aminocinnamic acid derivatives, the acyl auxiliary on the nitrogen is required to enable the substrate to form a chelate complex with rhodium.12 The mechanism of this reaction is shown in Fig. 22-3 the ligand in this case is DIPAMP (22-XV). 

In the case of an exothermic reaction the energy generated needs to be efficiently removed otherwise a runaway reaction could occur with potentially disastrous consequences. The catalyst itself may also be sensitive to even small increases in reaction temperature which may shorten its lifetime or result in a loss in reaction selectivity. The energy generated in an exothermic reaction may be recovered, often as steam, and used as a cost credit that energy has to be efficiently removed from the reaction section of the plant, again with impact on reactor design and cost. 

It is often useful to quickly estimate the maximum possible temperature rise, also known as the adiabatic temperature rise, in a catalyst pellet. Since no heat is transferred to the surroundings in this case, all energy generated (or consumed) by the reaction goes to heat (or cool) the pellet. The temperature difference between the surface and the pellet interior is directly related to the concentration difference. Dividing the material balance by the energy balance eliminates the reaction rate ... 

Advances in chemical reaction engineering and catalytic materials have allowed catalytic combustion for thermal energy generation to be commercialized in consumer and industrial applications. The development of catalysts coated on one side of a metal substrate, coupled with the use of diffusion barriers, has allowed controlling the combustion temperature to suit diverse applications. Catalytic materials have been developed to remain active for thousands of hours under conditions deemed too severe just a few years ago. We may expect that the need for clean distributed power increases the demand for gas turbines fitted with catalytic combustors and promotes the development of catalytic burners to be used in fuel processors for fuel cell power systems. 

The goal of maximum energy generation by oxidation of carbonaceous species often thwarted detailed examination of occasional selective oxidations, such as ethylene oxidation to acetaldehyde on Pd or Au (28, 29, 370) or to ethylene oxide on Ag (330) or methanol and benzyl alcohol oxidation to formates and benzaldehyde, respectively (6-32, 54, 250, 333). Product yields were usually determined at one potential only or even galvanostatically (330), and the combined effects of potential, catalyst, reactant concentration, and cell design or mixing on reaction selectivity are unknown at present. Thus, reaction mechanisms on selective electrocatalysis are not well understood with few exceptions. For instance, ethylene oxidation on solid pal-... 

Figure 27-1 Effect of the thermal energy generation paramete on dimensionless reactant concentration profiles as one travels inward toward the center of a porous catalyst with rectangular symmetry. The chemical kinetics are first-order and irreversible, and the reaction is exothermic. All parameters are defined in Table 27-4. The specific entries for P = 0.6 and = 1.0 are provided in Table 27-6.

Answer Two. The thermal energy balance is not required when the enthalpy change for each chemical reaction is negligible, which causes the thermal energy generation parameters to tend toward zero. Hence, one calculates the molar density profile for reactant A within the catalyst via the mass transfer equation, which includes one-dimensional diffnsion and multiple chemical reactions. Stoichiometry is not required because the kinetic rate law for each reaction depends only on Ca. Since the microscopic mass balance is a second-order ordinary differential eqnation, it can be rewritten as two coupled first-order ODEs with split boundary conditions for Ca and its radial gradient. 

Emission control is of the greatest importance in energy generation, and new high-performance catalysts play a key role here. For example, new catalysts that can decompose nitrous oxides into N2 and O2 would be of interest because the use of... 

X. Lin, C. Chen, J. Ma, X. Fang, Y. Zhan, Q. Zheng, Promotion effect of Nb for Cu/Ce02 water gas shift reaction catalyst by generating mobile electronic carriers, Int. J. Hydrogen Energy 38 (2013) 11841-11852. 

---