氮杂碳包铁负载钯催化苯甲醇无溶剂氧化

摘要

Using N-doped carbon-coated iron(Fe@NC) as the support,polyvinylpyrrolidone(PVP) as the stabilizer,a novel magnetically separable palladium nanoparticles supported on N-doped carbon-coated iron (Pd/Fe@NC) catalyst was prepared by the liquid phase reduction of palladium chloride acid and subsequent calcination method.The prepared catalysts were characterized by AAS,TEM,XRD and XPS.The effects of calcination temperatures,reaction temperatures,the catalyst amounts and alkali additives on the catalytic performance of the catalysts for the solvent-free oxidation of benzyl alcohol were investigated.The recycling performance of the catalyst was also studied.The results of AAS revealed that the loaded Pd mass fraction was 4.86%,which means Pd payload at a rate of 97.2%.TEM observation showed that Pd nanoparticles with a narrow size distribution and an average diameter of 5 nm were dispersed uniformly on the surface of Fe@NC support.Both XRD and XPS results confirmed that the active species on the surface of the catalyst consisted of Pd0,complexing Pd(Ⅱ) and PdO with lower contents.Under the condition of solvent-free,no alkali additive,O2 pressure 101.325 kPa (O2 flow rate 20 mL·min-1) and low catalyst amount [n(Pd)∶n(benzyl alcohol)=1∶2 000],Pd/Fe@NC catalyst could effectively catalyze the oxidation of benzyl alcohol.The conversion of benzyl alcohol and the selectivity to benzaldehyde were 86% and 87%,respectively,after reaction at 100 ℃ for 24 h.There was not any toxic substances produced in the process of reaction.As the complex Pd(Ⅱ) species partly converted into palladium in zero valence state,the catalytic activity was increased slightly after recycling 7 times.%以氮杂碳包铁(Fe@NC)为载体、聚乙烯吡咯烷酮为稳定剂,通过液相还原H2PdCl4和后续焙烧法制备新型的磁可分离Pd/Fe@NC催化剂,并进行AAS、TEM、XRD和XPS表征,将制备的催化剂用于苯甲醇无溶剂需氧氧化反应,考察焙烧温度、反应温度、催化剂用量和碱性助剂对其催化性能的影响,研究催化剂的循环使用性能.结果表明,Pd负载质量分数为4.86%,Pd有效负载比例为97.2%;Pd颗粒在载体上分散均匀,平均粒径为5 nm;催化剂活性物种组成包括Pd0和含量较低的络合Pd(Ⅱ)及PdO.在无溶剂、无碱性助剂、O2分压101.325 kPa(O2流量为20 mL·min-1)和低催化剂用量[n(Pd)∶n(苯甲醇)=1∶2 000]条件下,Pd/Fe@NC可高效催化苯甲醇的氧化反应,100 ℃反应24 h,苯甲醇转化率达86%,苯甲醛选择性为87%,反应过程中无任何有毒物质产生与排放.催化剂循环使用7次后,催化活性略有提高,催化过程中络合的Pd(Ⅱ)向Pd0的转化是其活性提高的主要原因.