Korean Chemical Engineering Research

  • 제55권2호
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  • Pages.270-274
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  • 2017
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  • 0304-128X(pISSN)
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  • 2233-9558(eISSN)
한국화학공학회 (The Korean Institute of Chemical Engineers)
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개미산 분해 반응에서 수소 생산성 증대를 위한 Pd/Pd3Fe 합금 촉매: 범밀도 함수 이론 연구

Pd/Pd3Fe Alloy Catalyst for Enhancing Hydrogen Production Rate from Formic Acid Decomposition: Density Functional Theory Study

  • 조진원 (한국과학기술연구원 연료전지연구센터) ;
  • 한종희 (한국과학기술연구원 연료전지연구센터) ;
  • 윤성필 (한국과학기술연구원 연료전지연구센터) ;
  • 남석우 (한국과학기술연구원 연료전지연구센터) ;
  • 함형철 (한국과학기술연구원 연료전지연구센터)
  • Cho, Jinwon (Fuel Cell Research Center, Korea Institute of Science and Technology (KIST)) ;
  • Han, Jonghee (Fuel Cell Research Center, Korea Institute of Science and Technology (KIST)) ;
  • Yoon, Sung Pil (Fuel Cell Research Center, Korea Institute of Science and Technology (KIST)) ;
  • Nam, Suk Woo (Fuel Cell Research Center, Korea Institute of Science and Technology (KIST)) ;
  • Ham, Hyung Chul (Fuel Cell Research Center, Korea Institute of Science and Technology (KIST))
  • 투고 : 2016.09.18
  • 심사 : 2016.12.22
  • 발행 : 2017.04.01
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초록

본 연구에서는 양자 역학 계산 이론 중 하나인 Density Functional Theory (DFT)를 사용하여 $Pd/Pd_3Fe$ 촉매 표면에서 개미산(HCOOH) 분해 반응으로부터 수소를 생산하는 반응 메커니즘을 분석하였다. 기존 연구에 따르면, 단일 원자 촉매 중에서 개미산 분해 반응에 가장 높은 수소 생산성을 기록하는 원자는 Pd 촉매이지만, 부 반응으로 생산되는 CO가 Pd에 독성을 띄우기 때문에 Pd 촉매의 성능을 저하시킨다. 이러한 단점을 극복하고자, Pd를 기반으로 Pd와 Fe를 3:1로 합금하여 $Pd_3Fe$가 코어(core) 형태로 존재하고 Pd가 표면에 위치한 core-shell $Pd/Pd_3Fe$ 촉매를 설계하여 개미산 분해 반응에 의한 수소 생산 속도를 계산하였다. 순수 Pd촉매 보다 $Pd/Pd_3Fe$ 촉매의 수소 생산 반응의 활성 에너지가 감소하였다. 그 이유는 Pd와 Fe가 합금화 되면서 $Pd_3Fe$의 격자 상수가 $2.76{\AA}$로 줄어 들어 HCOO의 흡착에너지를 0.03 eV 감소시켰고, Fe에서 표면 Pd로 전자가 이동하면서 표면 전자 구조가 변화하여 HCOO의 흡착에너지를 0.29 eV 낮추었기 때문이다. 본 연구에서 제안하는 결과를 바탕으로 추후 개미산으로부터 수소 생산이 더 용이한 새로운 촉매 설계 메커니즘을 제안하고자 한다.

Formic acid has been known as one of key sources of hydrogen. Among various monometallic catalysts, hydrogen can be efficiently produced on Pd catalyst. However, the catalytic activity of Pd is gradually reduced by the blocking of active sites by CO, which is formed from the unwanted indirect oxidation of formic acid. One of promising solutions to overcome such issue is the design of alloy catalyst by adding other metal into Pd since alloying effect (such as ligand and strain effect) can increase the chance to mitigate CO poisoning issue. In this study, we have investigated formic acid deposition on the bimetallic $Pd/Pd_3Fe$ core-shell nanocatalyst using DFT (density functional theory) calculation. In comparison to Pd catalyst, the activation energy of formic acid dehydrogenation is greatly reduced on $Pd/Pd_3Fe$ catalyst. In order to understand the importance of alloying effects in catalysis, we decoupled the strain effect from ligand effect. We found that both strain effect and ligand effect reduced the binding energy of HCOO by 0.03 eV and 0.29 eV, respectively, compared to the pure Pd case. Our DFT analysis of electronic structure suggested that such decrease of HCOO binding energy is related to the dramatic reduction of density of state near the fermi level.

키워드

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