醇类化合物的选择性氧化是实验室和工业应用中一类重要的官能团转化反应.以分子氧为氧化剂,在液相无溶剂条件下温和氧化符合绿色化学的要求.负载型Pd基催化剂因其优异的催化活性而在该反应中得到广泛应用.但是,单金属Pd催化剂对反应目标产物醛类化合物的选择性还有待提高.例如,在苯甲醇液相无溶剂氧化中,甲苯是在单金属Pd催化剂上的主要副产物.针对这一问题,除了对载体进行改性和修饰外,开发双金属Pd基催化剂也是一种有效的选择性调控策略.虽然已有的Pd-Au双金属催化剂可以在一定程度上降低甲苯的选择性,但是在较高温度和较高转化率下仍然难以控制甲苯的大量生成.本文采用固相合金化法合成了负载型Pd-Ni双金属纳米颗粒.该方法首先以硝酸镍为镍的前驱体浸渍介孔二氧化硅,然后负载钯纳米颗粒.在高温固相还原条件下,作为种子的钯纳米颗粒和镍通过原子迁移和生长,形成Pd-Ni双金属纳米颗粒.扫描透射电镜、能量色散X射线光谱、X射线衍射和X射线光电子能谱等表征证实了Pd-Ni双金属纳米颗粒的生成.上述催化剂用于苯甲醇液相无溶剂氧化,催化结果显示Ni的加入可以抑制副产物甲苯的生成,并且随Ni负载量增加,甲苯的选择性(在80%等转化率下)由22.6%(单金属Pd)降低至1.6%(双金属Pd1Ni20).尽管Ni的加入降低了单金属Pd的活性,但是由于提高了目标产物苯甲醛的选择性,醛的最终产率得到提升.进一步催化研究表明,Ni的加入可以抑制无氧氛围下甲苯的生成,说明Ni可以抑制歧化反应和降低表面氢浓度.这种作用可归结于Pd-Ni双金属的协同效应.该效应得到了CO吸附的傅里叶变换漫反射红外光谱和密度泛函理论研究的证实.双金属的几何效应和电子效应均减弱了苯甲醇在双金属纳米颗粒表面的解离吸附和相互作用,导致苯甲醇的吸附减弱,同时C–O键断裂不易进行.另外,由于Ni的亲氧性,双金属纳米颗粒表面有利于氧的吸附,降低吸附氢的浓度,减少C–H键生成,从而抑制甲苯的生成. The selective oxidation of alcohols is a kind of important functional group conversion reaction in laboratory and industrial applications.Molecular oxygenation as the oxidant and the mild oxidation in liquid solvent-free conditions are in line with the requirements of green chemistry.For the supported Pd-based catalysts, Excellent catalytic activity in the reaction has been widely used.However, the monometallic Pd catalyst for the reaction of the desired aldehyde compound selectivity has yet to be improved.For example, benzyl alcohol liquid solvent-free oxidation, toluene is a single metal Pd catalyst as the main byproduct.In view of this problem, in addition to the carrier modification and modification, the development of bimetallic Pd-based catalyst is an effective selective control strategy.Although the existing Pd-Au bimetallic catalyst can However, it is still difficult to control the mass production of toluene at higher temperature and higher conversion.In this paper, supported Pd-Ni bimetallic nanoparticles were synthesized by solid-phase alloying method. Mesoporous silica is first impregnated with nickel nitrate as a precursor of nickel and then loaded with palladium nanoparticles. Under high temperature solid-phase reduction conditions, palladium nanoparticles Pd-Ni bimetallic nanoparticles were formed by atomic migration and growth of nickel nanoparticles.The formation of Pd-Ni bimetallic nanoparticles was confirmed by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The above catalysts were used for the solventless oxidation of benzyl alcohol in the liquid phase. The catalytic results showed that the addition of Ni could inhibit the formation of toluene as a by-product, and the selectivity to toluene (at 80% conversion) increased from 22.6% Single metal Pd) was reduced to 1.6% (bimetallic Pd1Ni20) .Although the addition of Ni reduced the activity of monometallic Pd, the final yield of aldehyde was increased due to the increased selectivity of benzaldehyde as the target product.Further catalytic studies showed , Ni can inhibit the formation of toluene in an oxygen-free atmosphere, indicating that Ni can inhibit the disproportionation reaction and reduce the surface hydrogen concentration.This effect can be attributed to the synergistic effect of Pd-Ni bimetallic. Leaf transform diffuse reflectance infrared spectroscopy and density functional theory confirmed that both the geometric and electronic effects of bimetallic weaken the dissociative adsorption and interaction of benzyl alcohol on the surface of bimetallic nanoparticles, The adsorption of benzyl alcohol is weakened and the C-O bond is not easy to be broken.In addition, the surface of the bimetallic nanoparticles is favored for the adsorption of oxygen due to the affinity of Ni, which reduces the concentration of adsorbed hydrogen and reduces the formation of C-H bonds Inhibit the formation of toluene.