[학위논문]Ni, Fe) 촉매의 프로판 수증기 개질 반응 및 특성 분석 = Propane Steam Reforming and Characterization of La1-xSrxCr1-yMyO3-δ (M=Ni, Fe) Catalysts La1-xSrxCr1-yMyO3-δ (M원문보기
본 연구에서는 LaCrO₃를 기본으로 하는 perovskite형 물질을 SOFC의 연료극으로 사용하기 위하여 졸-겔법으로 촉매를 합성하였고, 프로판 수증기 개질반응을 통하여 촉매 활성을 평가하고, XRD, SEM, BET, ...
본 연구에서는 LaCrO₃를 기본으로 하는 perovskite형 물질을 SOFC의 연료극으로 사용하기 위하여 졸-겔법으로 촉매를 합성하였고, 프로판 수증기 개질반응을 통하여 촉매 활성을 평가하고, XRD, SEM, BET, TEM, H2-TPR을 이용하여 촉매 특성평가를 실시하였고, 전기화학실험을 통하여 다음과 같은 결론을 얻었다. 1. 졸-겔법으로 합성하고 1,000℃에서 소성한 촉매의 XRD결과 A-site의 Sr 치환양이 증가할수록 2차상(SrCrO₄)이 존재하였고, Sr 치환양이 감소할수록 2차상이 없는 perovskite 단일상을 얻을 수 있는 것은 킬레이트화 반응이 금속 양이온과 구연산 혹은 EDTA사이에서 관찰되기 때문이다. 2. SEM image을 통하여, 입자형태는 원형형태와 길게 뻗은 원통형으로 입자의 크기는 0.1 ~ 0.3 ㎛이고, 평균 BET 표면적은 ~4.7 ㎡/g 이다. 3. La_(1-x)Sr_(x)Cr_(0.9)Ni_(0.1)O₃의 프로판 수증기 개질반응을 통하여 S/C의 비가 1.7일 때, Sr 치환양이 0.2인 촉매가 높은 프로판 전환율과 수소 수율을 나타내었고, La_(1-x)Sr_(x)Cr_(0.7)Ni_(0.3)O₃은 Sr 치환양이 0.2인 촉매가, La1-xSrxCr0.5Ni0.5O₃은 Sr 치환양이 0.3인 촉매가 높은 활성을 나타냈다. 4. B-site의 Ni을 치환할 때 촉매 활성이 가장 좋은 La_(0.7)Sr_(0.3- )Cr_(0.5)Ni_(0.5)O₃ 촉매는 S/C의 비가 1.7일 때, 750℃에서 95.2 %, 83.7 %의 프로판 전환율과 수소 수율을 나타내었고, 800℃에서 100 %, 95.9 %의 프로판 전환율과 수소 수율을 나타내었다. 5. La_(0.7)Sr_(0.3 )Cr_(0.5)Fe_(0.5)O₃ 촉매는 800℃에서 95 %, 81.8 %의 프로판 전환율과 수소 수율을 나타내어 B-site에 Fe을 치환할 때 가장 좋은 촉매 활성을 나타내었지만, Ni을 치환했을 때만큼 촉매 활성을 나타내지 못하였다. 6. 수증기의 함량이 증가할수록 높은 프로판 전환율과 수소 수율을 나타내었고, B-site의 Ni와 Fe 치환양이 많은 촉매일수록 높은 촉매 활성을 보였다. 7. 프로판 수증기 개질반응 전 후의 촉매를 TEM image로 살펴본 결과 반응 전 입자의 크기는 SEM image와 같은 입자의 크기를 나타내었고, Niㅈ이 치환된 촉매가 Fe가 치환된 촉매보다 탄소 양이 많이 관찰되었으며, 반응 후의 입자는 filamentous carbon형태가 나타났다. 8. La_(0.7)Sr_(0.3)Cr_(1-y)Ni_(y)O₃ 촉매의 H₂-TPR profile은 약 300 ~ 380℃영역에서의 피크가 관찰되었다. Ni 치환양이 증가할수록 피크의 세기가 증가함을 나타냈다. La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ 촉매가 비교적 낮은 온도 영역에서 환원이 용이한 피크가 나온 것은 다른 금속과의 상호작용에 의해 환원 특성이 향상되어 프로판 전환율과 수소 수율에 크게 기여할 수 있었던 거라고 판단된다. 9. 직류 4단자법으로 전기 전도도 측정 결과, La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ 촉매의 전기 전도도는 800℃의 온도에서 4.0 S/cm( in air), 2.3 S/cm(in 5% H₂/N₂) 그리고 0.5 S/cm(in 5% C₃H_(8)/N₂)을 나타내었고, La_(0.7)Sr_(0.3-) Cr_(0.5)Fe_(0.5)O₃ 촉매는 800℃의 온도에서 6.7 S/cm(in air), 3.5 S/cm(in 5% H₂/N₂) 그리고 0.8 S/cm(in 5% C3H8/N2)을 나타냈다.
본 연구에서는 LaCrO₃를 기본으로 하는 perovskite형 물질을 SOFC의 연료극으로 사용하기 위하여 졸-겔법으로 촉매를 합성하였고, 프로판 수증기 개질반응을 통하여 촉매 활성을 평가하고, XRD, SEM, BET, TEM, H2-TPR을 이용하여 촉매 특성평가를 실시하였고, 전기화학실험을 통하여 다음과 같은 결론을 얻었다. 1. 졸-겔법으로 합성하고 1,000℃에서 소성한 촉매의 XRD결과 A-site의 Sr 치환양이 증가할수록 2차상(SrCrO₄)이 존재하였고, Sr 치환양이 감소할수록 2차상이 없는 perovskite 단일상을 얻을 수 있는 것은 킬레이트화 반응이 금속 양이온과 구연산 혹은 EDTA사이에서 관찰되기 때문이다. 2. SEM image을 통하여, 입자형태는 원형형태와 길게 뻗은 원통형으로 입자의 크기는 0.1 ~ 0.3 ㎛이고, 평균 BET 표면적은 ~4.7 ㎡/g 이다. 3. La_(1-x)Sr_(x)Cr_(0.9)Ni_(0.1)O₃의 프로판 수증기 개질반응을 통하여 S/C의 비가 1.7일 때, Sr 치환양이 0.2인 촉매가 높은 프로판 전환율과 수소 수율을 나타내었고, La_(1-x)Sr_(x)Cr_(0.7)Ni_(0.3)O₃은 Sr 치환양이 0.2인 촉매가, La1-xSrxCr0.5Ni0.5O₃은 Sr 치환양이 0.3인 촉매가 높은 활성을 나타냈다. 4. B-site의 Ni을 치환할 때 촉매 활성이 가장 좋은 La_(0.7)Sr_(0.3- )Cr_(0.5)Ni_(0.5)O₃ 촉매는 S/C의 비가 1.7일 때, 750℃에서 95.2 %, 83.7 %의 프로판 전환율과 수소 수율을 나타내었고, 800℃에서 100 %, 95.9 %의 프로판 전환율과 수소 수율을 나타내었다. 5. La_(0.7)Sr_(0.3 )Cr_(0.5)Fe_(0.5)O₃ 촉매는 800℃에서 95 %, 81.8 %의 프로판 전환율과 수소 수율을 나타내어 B-site에 Fe을 치환할 때 가장 좋은 촉매 활성을 나타내었지만, Ni을 치환했을 때만큼 촉매 활성을 나타내지 못하였다. 6. 수증기의 함량이 증가할수록 높은 프로판 전환율과 수소 수율을 나타내었고, B-site의 Ni와 Fe 치환양이 많은 촉매일수록 높은 촉매 활성을 보였다. 7. 프로판 수증기 개질반응 전 후의 촉매를 TEM image로 살펴본 결과 반응 전 입자의 크기는 SEM image와 같은 입자의 크기를 나타내었고, Niㅈ이 치환된 촉매가 Fe가 치환된 촉매보다 탄소 양이 많이 관찰되었으며, 반응 후의 입자는 filamentous carbon형태가 나타났다. 8. La_(0.7)Sr_(0.3)Cr_(1-y)Ni_(y)O₃ 촉매의 H₂-TPR profile은 약 300 ~ 380℃영역에서의 피크가 관찰되었다. Ni 치환양이 증가할수록 피크의 세기가 증가함을 나타냈다. La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ 촉매가 비교적 낮은 온도 영역에서 환원이 용이한 피크가 나온 것은 다른 금속과의 상호작용에 의해 환원 특성이 향상되어 프로판 전환율과 수소 수율에 크게 기여할 수 있었던 거라고 판단된다. 9. 직류 4단자법으로 전기 전도도 측정 결과, La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ 촉매의 전기 전도도는 800℃의 온도에서 4.0 S/cm( in air), 2.3 S/cm(in 5% H₂/N₂) 그리고 0.5 S/cm(in 5% C₃H_(8)/N₂)을 나타내었고, La_(0.7)Sr_(0.3-) Cr_(0.5)Fe_(0.5)O₃ 촉매는 800℃의 온도에서 6.7 S/cm(in air), 3.5 S/cm(in 5% H₂/N₂) 그리고 0.8 S/cm(in 5% C3H8/N2)을 나타냈다.
The most commonly used anode material for SOFCs is Ni/YSZ cermet, which displays excellent catalytic properties for H₂ oxidation and good current collection. Nevertheless, these also exhibit some disadvantages, such as low tolerance to sulphur and carbon deposition when using hydrocarbon fuels and p...
The most commonly used anode material for SOFCs is Ni/YSZ cermet, which displays excellent catalytic properties for H₂ oxidation and good current collection. Nevertheless, these also exhibit some disadvantages, such as low tolerance to sulphur and carbon deposition when using hydrocarbon fuels and poor oxidation stability which cause volume instability. In order to overcome the disadvantages of the Ni/YSZ cermet anode, LaCrO₃-based materials have been proposed. The introduction of other transition elements into the B-site of La_(1-x)Sr_(x)Cr_(1-y)M_(y)O_(3-δ)(M = Mn, Fe, Co, Ni) has been shown to improve the catalytic properties for methane reforming. In this paper, La_(1-x)Sr_(x)Cr_(1-y)M_(y)O₃-δ(M = Ni, Fe) catalysts were synthesized by citric acid and EDTA using the sol-gel method at pH 9. The catalysts were characterized by XRD, SEM, BET, TEM and H₂-TPR. The performance of catalytic activity in steam reforming of propane at temperature range 600 ~ 800℃ is investigated. The conductivity was measured by the four terminal d.c method in air, 5% H₂/N₂ and 5% C₃H_(8)/N₂. From the XRD pattern results, the main crystal structure of calcined samples was LaCrO₃. When the composition of Sr as substituent of La was 0.3 (La:Sr = 0.7:0.3), the secondary phase was observed, which means that impurity such as SrCrO₄ was formed. There were not any impurity phases as increasing the content of Sr to x=0.2 in the A-site, this may be because chelation is obtained between the constituent cations and citric acid or EDTA in the condition pH 9. The morphology of catalysts calcined at 1,000℃ consist of well separated particles and homogenous size in the submicron particles range between 0.1 ㎛ and 0.3 ㎛ of diameter from the SEM image, which agrees with the value determined from the TEM image. The reaction results were obtained using La_(1-x)Sr_(x)Cr_(1-y)M_(y)O_(3-δ )(M = Ni, Fe) catalysts under S/C=1.7 and S/C=1 reaction conditions, respectively. In both cases, propane conversion increased with an increase in the amount of added Sr upto x=0.3 in the A-site and Ni and Fe upto y=0.5 in the B-site. A similar trend was observed for hydrogen yield. Accordingly, La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ catalyst exhibited the best performance under Ni-substitution of which propane conversion was 100 % and hydrogen yield was 95.9 % at 800℃ in the S/C=1.7 condition. The La_(0.7)Sr_(0.3)Cr_(0.5)Fe_(0.5)O₃ catalyst exhibited the best performance under Fe-substitution of which propane conversion was 99.6 % and hydrogen yield was 81.8 % at 800℃ in the S/C=1.7 condition. H₂-TPR experiments were conducted to examine the reducibility of La_(0.7)Sr_(0.3)Cr_(1-y)Ni_(y)O₃ catalysts. For the Ni-substitution catalysts, one H₂-consumption peak(300 ~ 380℃) is observed. The peak at temperature is due to reduction of Ni^(3+) into Ni^(2+). The peak was replaced by an intense peak, when the amount of added Ni increased. This result indicates that Ni ions were more easily reduced in the large amount of Ni(y=0.5). The electrical conductivity of catalysts was measured by the 4-terminal D.C method. The electrical conductivity La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ catalysts in air, 5% H₂/N₂ and 5% C₃H_(8)/N₂ were measured as 4.0 S/cm, 0.3 S/cm and 0.5 S/cm at 800℃, respectively. The electrical conductivity La_(0.7)Sr_(0.3)Cr_(0.5)Fe_(0.5)O₃ catalysts in air, 5% H₂/N₂ and 5% C₃H_(8)/N₂ were measured as 6.7 S/cm, 3.5 S/cm and 0.8 S/cm respectively at 800℃. The measured electrical conductivity of catalysts under 5% H₂/N₂ was similar with reported results in the reference. The addition of Fe in B-site improved the electrical conductivity compared with that of Ni addition. Under 5% C₃H_(8)/N₂, the electrical conductivity was getting lower than that of H₂ and air condition.
The most commonly used anode material for SOFCs is Ni/YSZ cermet, which displays excellent catalytic properties for H₂ oxidation and good current collection. Nevertheless, these also exhibit some disadvantages, such as low tolerance to sulphur and carbon deposition when using hydrocarbon fuels and poor oxidation stability which cause volume instability. In order to overcome the disadvantages of the Ni/YSZ cermet anode, LaCrO₃-based materials have been proposed. The introduction of other transition elements into the B-site of La_(1-x)Sr_(x)Cr_(1-y)M_(y)O_(3-δ)(M = Mn, Fe, Co, Ni) has been shown to improve the catalytic properties for methane reforming. In this paper, La_(1-x)Sr_(x)Cr_(1-y)M_(y)O₃-δ(M = Ni, Fe) catalysts were synthesized by citric acid and EDTA using the sol-gel method at pH 9. The catalysts were characterized by XRD, SEM, BET, TEM and H₂-TPR. The performance of catalytic activity in steam reforming of propane at temperature range 600 ~ 800℃ is investigated. The conductivity was measured by the four terminal d.c method in air, 5% H₂/N₂ and 5% C₃H_(8)/N₂. From the XRD pattern results, the main crystal structure of calcined samples was LaCrO₃. When the composition of Sr as substituent of La was 0.3 (La:Sr = 0.7:0.3), the secondary phase was observed, which means that impurity such as SrCrO₄ was formed. There were not any impurity phases as increasing the content of Sr to x=0.2 in the A-site, this may be because chelation is obtained between the constituent cations and citric acid or EDTA in the condition pH 9. The morphology of catalysts calcined at 1,000℃ consist of well separated particles and homogenous size in the submicron particles range between 0.1 ㎛ and 0.3 ㎛ of diameter from the SEM image, which agrees with the value determined from the TEM image. The reaction results were obtained using La_(1-x)Sr_(x)Cr_(1-y)M_(y)O_(3-δ )(M = Ni, Fe) catalysts under S/C=1.7 and S/C=1 reaction conditions, respectively. In both cases, propane conversion increased with an increase in the amount of added Sr upto x=0.3 in the A-site and Ni and Fe upto y=0.5 in the B-site. A similar trend was observed for hydrogen yield. Accordingly, La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ catalyst exhibited the best performance under Ni-substitution of which propane conversion was 100 % and hydrogen yield was 95.9 % at 800℃ in the S/C=1.7 condition. The La_(0.7)Sr_(0.3)Cr_(0.5)Fe_(0.5)O₃ catalyst exhibited the best performance under Fe-substitution of which propane conversion was 99.6 % and hydrogen yield was 81.8 % at 800℃ in the S/C=1.7 condition. H₂-TPR experiments were conducted to examine the reducibility of La_(0.7)Sr_(0.3)Cr_(1-y)Ni_(y)O₃ catalysts. For the Ni-substitution catalysts, one H₂-consumption peak(300 ~ 380℃) is observed. The peak at temperature is due to reduction of Ni^(3+) into Ni^(2+). The peak was replaced by an intense peak, when the amount of added Ni increased. This result indicates that Ni ions were more easily reduced in the large amount of Ni(y=0.5). The electrical conductivity of catalysts was measured by the 4-terminal D.C method. The electrical conductivity La_(0.7)Sr_(0.3)Cr_(0.5)Ni_(0.5)O₃ catalysts in air, 5% H₂/N₂ and 5% C₃H_(8)/N₂ were measured as 4.0 S/cm, 0.3 S/cm and 0.5 S/cm at 800℃, respectively. The electrical conductivity La_(0.7)Sr_(0.3)Cr_(0.5)Fe_(0.5)O₃ catalysts in air, 5% H₂/N₂ and 5% C₃H_(8)/N₂ were measured as 6.7 S/cm, 3.5 S/cm and 0.8 S/cm respectively at 800℃. The measured electrical conductivity of catalysts under 5% H₂/N₂ was similar with reported results in the reference. The addition of Fe in B-site improved the electrical conductivity compared with that of Ni addition. Under 5% C₃H_(8)/N₂, the electrical conductivity was getting lower than that of H₂ and air condition.
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