二氧化硅负载型磷酸及磷酸二氢钠初始反应：试验和理论研究

利用XRD、TG、DRIFTS、^31 PMASNMR和密度泛函理论研究了浸渍法制各的硅胶负载型磷酸和磷酸二氢钠催化剂，阐明了催化剂制备过程中生成的初始缩合产物和其反应机理．光谱试验结果显示，存二氧化硅负载的磷酸上，除了聚磷酸外，还有硅磷酸盐的存在；在二氧化硅负载的磷酸二氢钠上，仅发现聚磷酸钠存在．密度泛函模拟结果也证明，磷酸与二氧化硅表面硅羟基之间的反应在缩合反应的初始阶段比其自身的二聚反应更为有利．但是在硅胶负载的磷酸二氢钠上，磷酸二氢钠的二聚和三聚是缩合反应初始阶段的主要反应．

The Initial Reactions of H3PO4 and NaH2PO4Supported on Silica: A Joint Experimental and Theoretical Study

A combination of X-ray powder diffraction, thermogravimetric analysis, diffuse reflection infrared Fourier transform, and ^31p magic-angle spinning nuclear magnetic resonance techniques with density function computation was used to elucidate the products and mecha- nism of the reactions among silica, H3PO4, and NaH2PO4 during the preparation of silica supported H3PO4 and NaH2PO4 catalysts. The spectral test results indicate that besides polyphosphoric acid, silicon phosphates on silica supported H3PO4 are also formed. On silica supported NaH2PO4 only sodium polyphosphates are present. Density functional theory （DFT） simulations indicate that in the initial stage, reaction of H3PO4 with silanol groups on the silica support is more favorable than that between H3PO4 itself. In contrast, dimerization and trimerization of NaH2PO4 are predicted to be the predominant initial reactions for the silica supported NaH2PO4 catalyst.