Highly selective catalysts for the hydrogenation of alkynols:A review

The semi-hydrogenation of alkynols to enols is a crucial process in the production of pharmaceuticals,agrochemicals,fragrances,and flavors that involves a complex set of parallel and consecutive isomerization and hydrogenation reactions and proceeds via several key intermediates.In view of the industrial importance of large-scale enol production through alkynol hydrogenation,various noble and non-noble metal(e.g.,Ni and Pd)-based catalysts promoting this transformation have been developed.This paper reviews the design of highly selective catalysts for the semi-hydrogenation of alkynols,focusing on the role of additives,second metals,catalyst supports,and reaction conditions and combining catalytic reaction kinetics with theoretical calculations to establish the reaction mechanism and the decisive factors for boosting selectivity.Finally,a strategy for designing highly efficient and selective catalysts based on the characteristics of aqueous-phase alkynol hydrogenation is proposed.

PdZn intermetallic compound stabilized on ZnO/nitrogendecorated carbon hollow spheres for catalytic semihydrogenation of alkynols

Enhancing the selectivity of noble metal catalysts through electronic modulation is important for academic research and chemical industrial processes.Herein,we report a facile sacrificial template strategy for the synthesis of PdZn intermetallic compound(3-4 nm)highly distributed in ZnO/nitrogen-decorated carbon hollow spheres(PdZn-ZnO/NCHS)to optimize the selectivity of Pd catalysts,which involves carbonization of a core-shell structured polystyrene(PS)@ZIF-8 precursor in an inert atmosphere,impregnation Pd precursor,and subsequent H2 reduction treatment.Due to the unique structural and compositional features,the developed PdZn-ZnO/NCHS delivers an excellent catalytic performance for the semihydrogenation of 2-methyl-3-butyn-2-ol(MBY)to 2-methyl-3-buten-2-ol(MBE)with high activity(>99%),high selectivity(96%),and good recyclability,outperforming the analog Pd on ZnO(Pd/ZnO)as well as the supported Pd nanoparticles(Pd/C and Pd/NC).Density functional theory(DFT)calculations reveal that the presence of Znδ+species in PdZn-ZnO/NCHS alters the adsorption modes of reactant and product,leading to a decrease of the adsorption strength and an enhancement of the energy barrier for overhydrogenation,which results in a kinetic favor for the selective transformation of MBY to MBE.In addition,PdZn-ZnO/NCHS was also very effective for the partial hydrogenation of dehydrolinalool to hydrolinalool.

Acidic Electrocatalytic Semihydrogenation of Alkynols to Alkenols on Copper Phosphide at Industrial-Level Current Density

Alkenols are important intermediates for the industrial manufacture of various commodities and fine chemicals.At present,alkenols are produced via thermocatalytic semihydrogenation of corresponding alkynols using precious metal Pd-based catalysts in pressurized hydrogen atmosphere.In this work,we highlight an efficient electrocatalytic strategy for selectively reducing alkynols to alkenols under ambient conditions.Using 2-methyl-3-butyn-2-ol as a model alkynol,Cu3P nanoarrays anchored on Cu foam remarkably deliver an industrial-level partial current density of 0.79 A·cm^(-2) and a specific selectivity of 98%for 2-methyl-3-buten-2-ol in acidic solution.Over a 40-runs stability test,Cu3P nanoarrays maintain 90%alkynol conversion and 90%alkenol selectivity.Even in a large two-electrode flow electrolyser,the single-pass alkynol conversion and alkenol selectivity of Cu3P nanoarrays exceed 90%.Moreover,this selective electrocatalytic hydrogenation approach is broadly feasible for the production of various water-soluble alkenols.Electrochemical analyses,theoretical simulation and electrochemical in-situ infrared investigations together reveal that exothermic alkynol hydrogenation,facile alkenol desorption and formation of active H on Cu3P surfaces account for the excellent electrocatalytic performance.

Influence of Pd deposition pH value on the performance of Pd-CuO/SiO_(2) catalyst for semi-hydrogenation of 2-methyl-3-butyn-2-ol(MBY)

The selective hydrogenation of C≡C to C=C bonds is an important step,yet remains to be a great challenge in chemical industry.In this study,we have revealed the influence of Pd deposition pH value on the catalytic performance of Pd-CuO/SiO_(2)catalyst for the semi-hydrogenation of 2-methyl-3-butyn-2-ol(MBY).Trace amount of Pd(about 500 ppm)was loaded via deposition-reduction method on CuO/SiO_(2)support by using H_(2)PdCl_(4) solution as precursor and NaBH_(4)as reductant,respectively.The pH value at which Pd was deposited was adjusted to about 5 and 7 by adding NaOH solution.The obtained catalysts were characterized by several techniques including XRD,TEM,H_(2)-TPR,etc.In the case of pH value of 5,the CuO was partially dissolved during the deposition and then co-reduced with Pd^(2+)by NaBH_(4),forming PdCu alloy structure in sub-nanometer.In contrast,no PdCu alloy structure was observed when pH value was 7.The kinetics of MBY semi-hydrogenation over both catalysts were compared.The former PdCu alloy catalyst showed very high selectivity towards the semi-hydrogenation of MBY due to its low activity in hydrogenation of C=C bond in 2-methyl-3-buten-2-ol(MBE).The results herein demonstrated that the pH value where Pd was deposited played a crucial role in determining the catalytic performance of PdCu catalyst.