Selective Hydrogenation Of Citral Over MOF-derived Pt@Co-MOF And Pt/Co@C

As a fine chemical intermediate,geraniol and nerol have a pivotal position in the chemical industry,especially in terms of flavors,fragrances and medical drugs.As an important?,?-unsaturated aldehyde,citral is mainly derived from Fengmao oil and Litsea cubeba oil.Its selective hydrogenation to geraniol and nerolitol has been proved to be one of the most economical and ideal routes.However,it is worth noting that the direct hydrogenation of unsaturated aldehydes to produce saturated carbonyl compounds is relatively easy,and the conversion to unsaturated alcohols is more challenging.This is mainly because the hydrogenation of a carbonyl group is thermodynamically less favorable than that of a C=C double bond conjugate to the carbonyl present in citral,so that the carbon-carbon double bond is more easily hydrogenated to directly produce a saturated carbonyl compound.According to the current reports,the catalysts used for selective hydrogenation of citral to produce unsaturated alcohols are basically heterogeneous catalysts.The catalytic substrates mainly include silica,activated carbon,carbon nanotubes and aluminium trioxide.The catalytic active metals mainly contain Co,Ru,Pt and Ir.While the catalytic carrier and the metal active center have weaker force,the metal content is lower,and the metal active center is easy to aggregate,which seriously hinders the production of unsaturated alcohol.Therefore,it is desirable to prepare an efficient and recyclable catalyst for the selective hydrogenation of citral with high conversion and selectivity.Metal–organic frameworks?MOFs?,constructed by organic linkers and metal nodes,are a new class of crystalline porous materials with significant application potentials.Compared with traditional inorganic porous materials,Featured with extremely high surface area,large porosity,tunable pore size,and flexible functionality,MOFs have gained extensive explorations as a highly versatile platform for functional applications in many research fields.At the same time,its clear and tunable crystalline structure provides an ideal platform for the study of the structure-activity relationship of materials,making MOFs show great advantages in both basic research and practical applications.Based on the specificity of MOFs materials,People have aroused great interest in the construction of nanocatalysts?the characteristics of catalytically active nanoparticles confned into the cavities/channels of MOFs or surrounded by MOFs?and MOFs are used as templates and precursors to transform into more stable conductive carbon/metal-based porous materials than MOFs,while also retaining the properties of the original MOFs.The content of this paper can be divided into two parts:1.Using large surface area and strong adsorption properties of MOFs,we successfully prepared Pt@Co-MOF-X?X stands for the temperature of reduction?composites by one-pot method.Under the action of MOFs material,even high temperature reduction under hydrogen atmosphere,the metal nanoparticles are still more evenly wrapped by MOFs and the size is about 3.3 nm.In the test of citral hydrogenation,the conversion and selectivity of Pt@Co-MOF-200?composite for citral reached 50%and 100%under the reaction conditions of 80?,60 min and 1MPa H₂,and the catalyst could be recycled for 8 times with good stability.2.Pt/Co@C-X?X represents the temperature of pyrolysis?composite was successfully prepared by in-situ pyrolysis of the above precursor under high temperature in a nitrogen atmosphere.Even at high temperatures,the metal nanoparticles are still more uniformly encapsulated by a highly graphitized carbon layer and have a size of about 16 nm.In the test of citral hydrogenation,the conversion and selectivity of Pt/Co@C-500?composite for citral reached 100%and 72%under the reaction conditions of 110?,60 min and 1 MPa H₂,and the catalyst could be recycled for 4 times with good stability.