| Selective catalytic hydrogenation,including direct hydrogenation using high-pressure H2,photocatalytic and electrocatalytic hydrogenation using active charge,is widely used in both petrochemical and fine chemical industries,and how to develop the low-cost and efficient catalysts is attracting but challenging.Generally,hydrogenation reaction using H2 involves three major steps:（i）H2 adsorption and dissociation on the catalyst surface,（ii）substrate adsorption on the catalyst surface,and（iii）dissociated H spillover and reaction.The overall activity of hydrogenation reaction is mainly determined by the（i）and（iii）steps,whereas the selectivity is determined by the（ii）step.Therefore,the key for the design and construction of efficient hydrogenation catalysts lies in promoting the efficiencies of above three steps.For the photocatalytic and electrocatalytic hydrogenation under room temperature and atmosphere,catalysts are critical to adsorb and activate the substrates for proton-coupled electron transfer,which determines the hydrogenation selectivity.Carbon-based catalysts are attracting intensive attention because they are inexpensive,stable,and environmentally friendly.In Chapter 2,we report the inert carbon can be activated as metal-like hydrogenation catalyst for the nitroarene hydrogenation.DFT calculations predict that P dopants and accompanied lattice defects in carbon matrix can significantly delocalize the electron and change the band structure to a metal-like one,and thus both H2 and the nitro group are easily activated for selective hydrogenation.Experimentally,we synthesize this carbon catalyst with tunable concentration of P-dopant and lattice defect by polymerization and carbonization of phytic acid,and find the concentration of lattice defect is closely related to that of P-dopants.The obtained catalyst exhibits good catalytic activity,perfect selectivity,and stability in the hydrogenation of nitroarenes,surpassing the reported metal-free,metal-oxide,and nickel catalysts.moreover,the hydrogenation activity is linearly dependent on the P-doping and/or defect concentration,in consistent with DFT calculation.Considering the activity of single doped carbon catalysts is unsatisfied due to the sluggish H2 dissociation,the synergistic effect of composites may overcome the problem by taking advantage of the perfect selectivity of nitro group adsorption over doped carbon.One promising approach is involving an active phase tawords H2dissociation.With this consideration,we construct Co nanoparticles encapsulated in N-doped carbon（Co@NC）by pyrolysizing the mixture of Co salt,and carbon nitride.A yield with a TOF of～12.3 h-1 and a selectivity to 4-aminophenol of>99.9%was obtained for the hydrogenation of 4-nitrophenol at room temperature and 10 bar H2pressure.The superior catalytic performance can be attributed to a cooperative effect between electron-deficient Co nanoparticles for hydrogen activation and electron-rich N-doped carbon for an energetically preferentially adsorption of nitroarenes via nitro group.Additionally,we construct the highly dispersed Ni2P supported on P-doped carbon and take the advantages of ultradispersed Ni2P nanoclusters and P-doped carbon.As a synergistic result,the synthesized catalyst delivers high activity and selectivity chemoselective hydrogenation of nitroarenes,and outperforms various noble-and transition-metal catalysts.Moreover,we find the d-band center of Ni downshifts due to the nanometer effect,which promotes H desorption on highly charged antibonding orbital of Ni-H.For selective hydrogenation of chemicals,the high selectivity is always at the expense of activity and improving both selectivity and activity is challenging.By chelating with p-fluorothiophenol（SPhF）-arrays,both steric and electronic effects are created to boost the performance of inexpensive nickel-based catalysts.Compared with Ni2P,SPhF-chelated one exhibits nearly 12-times higher activity and especially its selectivity is increased from 38.1%and 21.3%to nearly 100%in hydrogenations of 3-nitrostyrene and cinnamaldehyde.Commercial catalyst like Raney Ni chelating with SPhF-array also exhibits an enhanced selectivity from 20.5%and 23.4%to～100%along with doubled activity.Both experimental and DFT calculation prove the superior performance is attributed to the confined flat adsorption by ordered SPhF-arrays and downshifted d-band center of catalysts,leading to prohibited hydrogenation of vinyl group and accelerative H2 activation.Hydrogen peroxide is a highly valuable chemical,and electrocatalytic oxygen hydrogenation towards H2O2 offers an alternative method for safe on-site applications.Generally,low-cost hematite is not recognized as an efficient electrocatalyst because of its inert nature,but we herein report thatα-Fe2O3 can be endowed with high catalytic activity and selectivity via the engineering of facets and oxygen vacancies.DFT calculations predict that the{001}facet is intrinsically selective for H2O2 production,and that oxygen vacancies can trigger the high activity,providing sites for O2 adsorption and protonation,stabilizing the*OOH intermediate,and preventing cleavage of the O-O bond.The synthesized oxygen-defectiveα-Fe2O3 single crystals with exposed{001}facets achieved high selectivities for H2O2 of>90%,>88%,and>95%in weakly acidic,neutral,and alkaline electrolytes,respectively,and the H2O2 production rate reached454 mmol g-1cat h-1 at 0.1 V vs.RHE under alkaline conditions.In an anion exchange membrane fuel cell（AEMFC）,a maximum H2O2 production of 546.8 mmol L-1 with a high Faradaic efficiency of 80.5%was achieved. |
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