First-principles Study Of Ethyl Acetate Synthesis From Ethanol One-pot Reaction On Copper Alloys

Ethanol dehydrogenation dimerization to form ethyl acetate(EA)and hydrogen is,in principle,the best atomically economic reaction and is also considered to be an environmentally friendly process in EA synthesis.Copper-based catalysts are the only commercial catalysts.However,it has some drawbacks,such as low productivity for EA and difficult separation from the by-products,such as acetaldehyde,butyraldehyde,butanol and so on.Alloying is investigated in this work to increase the catalytic performance of copper-based catalysts.To start with,density functional theory was used to investigate the ethanol dehydrogenation dimerization on Cu(111).This work used the trial-and-error method to calculate and analyse the reaction network on Cu(111)along different dehydrogenation pathways.Based on the calculated energy barriers and reaction rate constants,it was found that the process of ethanol first dehydrogenation is not through hydroxyl dehydrogenation and ?-CH dehydrogenation is the feasible pathway,which replenishes the reaction mechanism proposed by Colley.Additionally,the process that both CH3 CHOH and CH3 COH combine with ethoxy was studied.The results indicate the possibility of hemiacetal formation.This provided a theoretical foundation for Inui route and expanded the previous studies on the reaction mechanism of ethanol dehydrogenation to EA on Cu(111).Moreover,the periodic surface models of Cu3Pt(111)and Cu3Pd(111)were built to study the alloying effect on the ethanol dehydrogenation reactions.Then the trial-and-error method was used to calculate and analyse the reaction network of ethanol dehydrogenation to EA on Cu3Pt(111)and Cu3Pd(111).The DFT results showed that the addition of Pd or Pt reduces the energy barriers of ethanol dehydrogenation.The reaction rate constants for ethanol ?-C-H dehydrogenation on Cu3Pt(111)and Cu3Pd(111)are 697.5 and 2447.5 times of those on Cu(111),respectively.Therefore,the addition of Pd or Pt increases the reaction rate of ethanol dehydrogenation and thus improves ethanol conversion rate.The adsorption energies of the acetaldehyde on Cu3Pt(111)and Cu3Pd(111)are-0.27 eV and-0.24 eV while that on Cu(111)is-0.18 eV.This implies that the addition of Pd or Pt contributes to the strong adsorption of the acetaldehyde.On the other hand,the energy barriers of acetaldehyde dehydrogenation to acetyl on Cu3Pt(111)and Cu3Pd(111)are 0.27 eV and 0.11 eV,respectively,which are lower than that of Cu(111).In a word,copper alloyed with Pt and Pd improves ethanol conversion rate,but lowers EA's selectivity,especially Pt due to the formation of CH2 CHOH.Finally,reaction rate constants,the reaction equilibrium constants were also calculated.For hydrogen formation,the equilibrium constant on Cu3Pt(111)and Cu3Pd(111)is 21568 times and 8351 times of that on Cu(111).For EA formation,the equilibrium constant on Cu3Pt(111)and Cu3Pd(111)is 0.07 percent and 2.5 times as much as that of Cu(111).Combining the results of adsorbates' adsorption,energy barriers,reaction rate constants and equilibrium constants,Cu3Pd(111)is the best catalyst for ethanol hydrogenation to EA and H2 among the three catalysts studied here.