H_(2)O对CaO硫化反应加速作用机理研究

Study on the Acceleration Mechanism of H_(2)O to CaO Sulfation

通过实验和密度泛函理论,研究了水对CaO硫化反应加速作用的机理。实验结果显示,水对快速硫化反应阶段影响微弱,而慢速反应阶段水的加入会立刻提高反应速率。DFT计算表明,CaO表面生成CaSO_(4)产物层的能垒小于H_(2)O在CaO表面解离的能垒,可能是水对快速硫化反应阶段作用微弱的原因。无水情况下慢速反应阶段的控制步骤不是CaO和CaSO_(4)晶体内的固态离子扩散,而是在原产物层上生成新产物层时,CaSO_(4)表面Ca^(*)离子向新产物层扩散的过程,其能垒为3.61eV。吸附于CaSO_(4)表面的H_(2)O分子解离为H*和OH*后,将CaSO_(4)表面Ca^(*)离子向新产物层扩散的能垒降低了1.98eV,使慢速反应阶段决速步变为O^(2-)在CaSO_(4)晶体内的扩散,有水情况下硫化反应整体控制步骤能垒相比于无水情况降低了0.19eV,以此加速硫化反应。

The microcosmic mechanism of the accelerating effect of water on CaO sulfation reaction was studied by the experiment and density functional theory.The results show that the addition of water in the slow reaction stage immediately increases the sulfation rate.The energy barrier of the formation of CaSO_(4) product layer on CaO surface is smaller than that of H_(2)O dissociation,which may be the reason that water has no acceleration effect in the rapid reaction stage.In the anhydrous condition,the control step in the slow reaction stage is not the diffusion of solid-state ions in CaO and CaSO_(4) crystals,but the diffusion process of calcium ions on the original CaSO_(4) surface to the newly formed CaSO_(4) product layer,whose energy barrier is 3.61eV.In the hydrous condition,after the H_(2)O molecule adsorbs on the CaSO_(4) surface and dissociates into H^(*) and OH^(*) with an energy barrier of 2.91eV,the energy barrier of the control step of anhydrous condition is reduced by 1.98eV,and the rate-limiting step for the hydrous condition changes to the diffusion of O^(2-) in the CaSO_(4) crystal,whose energy barrier is 0.19eV lower than the rate-limiting step of the anhydrous condition.