Numerical Simulation of Monolithic Catalysts with a Heterogeneous Model and Comparison with Experimental Results from a Wood‐fired Domestic Boiler

An increased utilization of biomass for heat and power production contributes to reduced emission of the greenhouse gas CO₂. However, when combusted in small‐scale units, such as domestic stoves and boilers, the emissions of unburned gases, i.e. CO and light and heavy hydrocarbons, tend to be high. An attractive solution to reduce these emissions is the integration of oxidation catalysts. In this paper the development of a multidimensional heterogeneous mathematical model for the simulation of one channel in a monolithic catalyst is presented. The results of the simulation are compared with experimental data from a wood fired domestic boiler in which a monolithic catalyst has been integrated. The results show that the mass transfer inside the channels limits the conversion and that segmentation of the monolithic catalyst may therefore significantly increase the conversion. A good agreement between the simulation and the experimental data was achieved, for both the segmented and the unsegmented catalyst, and the model was proven to be a valuable tool for the optimization of the catalyst design.     

Chemical Reactions in the Exhaust System of a Cold‐start Engine

Transient heat transfer and water condensation in the engine exhaust system have a strong influence on the conversion of carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO_x) in the three‐way catalytic converter (TWC) of an engine cold‐start. This paper presents the theoretical modeling of heat transfer and chemical reactions of CO, HC, and NO associated with the effects of catalyst surface water vapor condensation, and water evaporation in the entire engine exhaust system fitted with a TWC. The predictive capability of the model is validated successfully with the experimental data.     

Dual‐bed Catalytic System for the Selective Reduction of NOx with Propene

For the removal of NO_x from exhausts containing excess oxygen, the selective catalytic reduction of NO_x using hydrocarbons (HC‐SCR) is highly interesting, especially for car applications (lean deNO_x) [1]. Two types of HC‐SCR catalysts can be distinguished. High‐temperature catalysts operate at temperatures above 573 K, showing moderate activity, and (mostly) low heat and poison resistance, but high N₂ selectivity. Low‐temperature catalysts, usually based on Pt, operate between 473 and 573 K, showing opposite features: very high activity, as well as heat and poison resistance, and a low N₂ selectivity by forming N₂O. Our strategy for developing an active and stable deNO_x system without N₂O emission is the implementation of a separate catalytic function for N₂O removal as a second stage.     

A Note on Factorial Designs for Kinetic Investigations of Heterogeneous Catalytic Reactions in Differential Recycle Reactors

A study was performed to demonstrate that reliable values for the kinetic parameters can be determined from kinetic data obtained experimentally by simply varying the inlet mole fractions according to a factorial design. As demonstrated by simulation calculations and experiments in such a case one can dispense with a concentration control strategy thus considerably reducing the necessary expenditure of time and apparatus.     

‘High Conductivity’ Monolith Catalysts for Gas/Solid Exothermic Reactions

The replacement of conventional packed beds of catalyst pellets with novel ‘high conductivity’ honeycomb catalysts in industrial externally cooled multitubular fixed‐bed reactors for exothermic gas/solid processes offers potential advantages besides reduced pressure drops. Near‐isothermal operation could result in safer reaction operation, better catalyst thermal stability, improved selectivities, higher throughputs and more economical reactors with larger tubes. We report herein an experimental and theoretical investigation of this concept.     

铑在不同载体材料上的分配比对低含量贵金属催化剂性能的影响

采用浸渍法制备了一系列低Pt、Rh含量的Pt-Rh型汽车尾气净化催化剂.研究了在Pt、Rh含量一定以及其他条件不变的情况下,只改变铑在不同栽体上的分配比对催化剂性能的影响,测定了催化剂对C3H8、CO、NO的起燃温度,并对催化剂样品进行了程序升温还原(H2-TPR)、程序升温脱附(O2-TPD)表征.结果表明:新鲜催化剂对C3H8、CO、NO的起燃温度相差不大,但经过1000℃、5h的水热老化后,催化剂性能发生了显著的变化,C3H8、CO、NO的起燃温度出现较大的差异,说明了铑在不同栽体上的分配比对催化剂性能有一定影响,特别是对催化剂的抗老化性能影响较大.     

低压甲醇羰基化制醋酸用Ni系催化剂及其制备工艺

介绍了用于低压甲醇碳基化制醋酸的Ｎｉ系催化剂进展概况。讨论了浸渍法制备Ｎｉ催化剂的工艺条件：催化剂中Ｎｉ含量以２．５％为宜；添加助剂和选择性能好的载体可提高Ｎｉ系催化剂的活性，助剂以Ｍｏ、Ｃｏ居多，载体以活性炭和碳分子筛为佳。在碳基化反应中，加入助催化剂（如碘甲烷）和氢气可提高催化剂的活性和选择性。提出了Ｎｉ系催化剂开发的两个主要方向。