The simultaneous processes of diffusion, adsorption and chemical reaction, considering the transient nature of the concentration profiles in the porous catalyst particles as applied to the analysis of consecutive reactions A → B → C , where reactant and products are subjected to diffusion limitations, are analyzed. The concentrations of the desired intermediate product B , both the average in the catalytic particles and the observed in the fluid phase, initially increase as a function of time until reaching a maximum value and then decline due to the consumption in the secondary reaction. Due to the diffusion restrictions and the adsorption effect, the observed selectivities, calculated from the concentrations in the fluid phase, are always lower than the true selectivities, which also include the amounts accumulated in the particles. Besides depending on the rates of the primary and secondary reactions, the observed yield of product B also depends on the system adsorption capacity, i.e., the relationship between the capacities of the particles and the external fluid phase to accumulate the reactant species. For a given relationship between the intrinsic rates of the primary and secondary reactions, the higher the system adsorption capacity, the lower the observed yield of B as a function of conversion. The relationship between the observed yield of B and the observed conversion of A , calculated considering the transient state of the concentration profiles in the particles, is coincident with that predicted by classical models, which assume the steady state in the particles, when the system adsorption capacity is extremely small.

中文翻译：

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非稳态扩散-吸附-反应。多孔催化剂颗粒上连续反应的选择性

分析了扩散、吸附和化学反应的同时过程，考虑到多孔催化剂颗粒中浓度分布的瞬态特性，应用于分析连续反应 A → B → C，其中反应物和产物受到扩散限制. 所需中间产物 B 的浓度，即催化颗粒中的平均值和液相中观察到的浓度，最初随时间增加，直到达到最大值，然后由于次级反应中的消耗而下降。由于扩散限制和吸附效应，观察到的选择性，根据液相中的浓度计算，总是低于真实选择性，其中还包括颗粒中积累的量。除了取决于初级和次级反应的速率外，观察到的产物 B 的产率还取决于系统吸附能力，即颗粒与外部流体相积累反应物种类的能力之间的关系。对于初级和次级反应的固有速率之间的给定关系，系统吸附容量越高，观察到的 B 收率作为转化率的函数越低。观察到的 B 产率和观察到的 A 转化率之间的关系，考虑到颗粒中浓度分布的瞬态计算，与经典模型预测的一致，经典模型假设颗粒中的稳态，当系统吸附时容量极小。