This work shows for the first time that palladium chloride, PdCl₂, can influence the sequencing of sol–gel reactions involving tetraethyl orthosilicate (TEOS). A three-step procedure was utilised to create porous silica materials: liquid-phase sol reaction, drying and calcination. Evidence from ¹H Nuclear Magnetic Resonance (NMR) spectroscopy revealed that PdCl₂ had negligible influence on liquid-phase sol–gel reactions. During drying, ²⁹Si NMR data showed that the silica sols doped with PdCl₂ underwent more condensation reactions than those without. Variations in parameters known to effect sol–gel reactions could not account for the magnitude of the observed changes. Evidence from differential scanning calorimetry indicates that palladium catalyses silica hydrolysis during the drying stage, which promotes condensation reactions. Despite being more condensed after drying, ²⁹Si NMR analysis revealed that the palladium silica structure became less condensed (compared with non-doped silica) after calcination. It is hypothesised that the interaction between palladium oxide and silanol groups inhibits condensation during the calcination process. The differences in sol–gel bonding seems to have minimal influence on the porosity of the calcined materials, though the presence of palladium nanoparticles reduced the total pore volume. This work has important implications for the design and optimisation of porous palladium silica materials. It also challenges the common assumption that metal dopants do not interact with silica sol–gel reactions.

Differential scanning calorimetry analysis of silica (Si06) and palladium doped silica (PdSi06) xerogels prepared via sol–gel. The PdSi06 material exhibits no exothermic peak between 300 and 500 °C. This is indicative of the catalytic effect of aqueous palladium species on sol–gel hydrolysis reactions.

这项工作首次表明，氯化钯PdCl ₂可以影响涉及原硅酸四乙酯（TEOS）的溶胶-凝胶反应的顺序。利用三步法制备多孔二氧化硅材料：液相溶胶反应，干燥和煅烧。¹ H核磁共振（NMR）光谱的证据表明，PdCl ₂对液相溶胶-凝胶反应的影响可忽略不计。在干燥过程中，²⁹ Si NMR数据表明硅溶胶中掺有PdCl ₂发生的缩合反应比没有的发生更多。已知会影响溶胶-凝胶反应的参数变化无法解释观察到的变化的幅度。差示扫描量热法的证据表明，钯在干燥阶段催化二氧化硅的水解，从而促进缩合反应。尽管干燥后更凝结，²⁹Si NMR分析表明，煅烧后，钯二氧化硅的结构变得较少冷凝（与未掺杂的二氧化硅相比）。假设在煅烧过程中氧化钯与硅烷醇基团之间的相互作用抑制了缩合。溶胶-凝胶键合的差异似乎对煅烧材料的孔隙率影响很小，尽管钯纳米颗粒的存在降低了总孔体积。这项工作对多孔钯二氧化硅材料的设计和优化具有重要意义。这也挑战了金属掺杂剂不会与硅溶胶-凝胶反应相互作用的普遍假设。

通过溶胶-凝胶法制备的二氧化硅（Si06）和掺杂钯的二氧化硅（PdSi06）干凝胶的差示扫描量热分析。PdSi06材料在300至500°C之间没有放热峰。这表明钯水溶液对溶胶-凝胶水解反应的催化作用。