Studies on the cell performance of MEA with Pt-loaded ETS-10-based electrode in PEMFCs

황지영 건국대학교 대학원 2009 국내석사

Microporous titanium silicate, ETS-10 was used as a supporting material for Pt in anode of PEMFC. Pt-ETS-10 was successfully obtained by 2-step ion-exchange processes. (Na+K)-ETS-10 was first ion-exchanged to H-ETS-10 using hydrochloric acid solution and so obtained H-ETS-10 was further ion exchanged to Pt complex-ETS-10 using [Pt(NH₃)₄] salt solution, which was then reduced to Pt-ETS-10 by NaBH₄solution. XRD analysis indicated that the structure of ETS-10 was still maintained through ion-exchange processes. EDS and TEM analyses showed that Pt particles were uniformly dispersed within ETS-10. The Pt loading of Pt-ETS-10 was 1.6 wt.%. Commercial Pt/C and obtained Pt/Z were used for composite electrochemical catalyst layer for anode in PEMFC. The catalyst materials (Pt/C and Pt/Z), D.I. water, IPA, and Nafion dispersion solution were ultrasonicated to prepare catalyst ink. The prepared catalyst ink was then sprayed onto GDLs to fabricate composite catalyst layer. The composite catalyst layer was carefully controlled to maintain 0.3mg/cm² of Pt for anode catalyst. Commercial GDE based carbon cloth was used as cathode (0.5 mg/cm2), and Nafion 115 membrane was used for electrolyte of MEAs. MEA was assembled by hot-pressing Pt-Z containing anode, commercial cathode and membrane between them at 135℃ for 3 mins. The cell performance was measured at 80℃. The composite catalyst layers were fabricated by three-methods . Mixed catalyst layer, GDL-C-Z method, and GDL-Z-C method. Mixed catalyst layer was fabricated by mixing Pt/C and Pt/Z catalyst powders. However, alternative layers were fabricated by coating Pt/C catalyst onto GDL on which Pt/Z was then coated, or vice versa. The results show that the effect of the composition of Pt/C and Pt/Z has a significant effect on cell performance regardless of fabrication method of electrode; that is, the power density of MEA fabricated with the composition of 70:30 in % wt of Pt/C:Pt/Z shows the highest. Regarding the effect of fabrication method on cell performance, the MEA fabricated with CZC method where the Pt/Z layer was first coated onto GDL and the Pt/C was then coated onto Pt/Z layer showed that the dependency of power density on the composition of Pt/C and Pt/Z is not as high as two previous cases. This might be ascribed to the enhanced electrochemical reaction throughout two different catalyst layers and lower ohmic power loss due to hydrophilic nature of zeolite at the hydrogen feed side. In addition, the result shows that the CCZ method has maintained its power density higher than of the other two cases at high current density.

An Investigation of Chemical Fixation of CO2 into Cyclic Carbonates over Metal Oxide, Ionic Liquid and Carbonaceous Catalysts

Mujmule Rajendra Basavant 명지대학교 대학원 2021 국내박사

Currently, it is essential to consider the rapidly increasing emission of carbon dioxide (CO2) into the atmosphere. CO2 is produced from the aerobic combustion of carbon-containing material. It is hugely produced from fossil fuel combustion and is considered the most major greenhouse gas. Now, CO2 capture and utilization from flue gases are being considered as the best option to mitigate the greenhouse effect for the industrial combustion process. Researchers have focused their efforts on the successful conversion of CO2 into high-value chemicals and feedstocks due to a significant rise in atmospheric CO2 over the years and the potential environmental risk such as climate change and ocean acidification. However, the CO2 conversion is still challenging due to its thermodynamically stable and kinetically inert nature. The development of a suitable catalyst system could partially help to overcome this issue. Catalyst is the crucial tool that successfully used to achieve the transformation required for the synthesis of chemicals. This reduces the cost of production and enhances the atom economy of the reaction. In this regard, developing an effective and straightforward catalytic system for the chemical fixation of CO2 from an ecological and economic point of view has been a critical task to the research community. Encouraging by this fact, we established efficient and straightforward catalytic systems (metal oxide, ionic liquid and carbonaceous-based catalyst system) from naturally abundant, inexpensive, environmentally friendly and commercially available precursor materials for the direct conversion of CO2 into a valuable product such as cyclic carbonates. The cycloaddition reaction of CO2 and epoxides into cyclic carbonates, which are valuable products due to their wide range of applications such as electrolytes in batteries, polar aprotic solvent, monomers for polymer synthesis, intermediates pharmaceutical and fine chemical industry. Subsequently, transition metal oxides (TMOs) have attracted much researchers attention due to their applications in various fields. They are also getting importance as a Lewis acid-base catalyst. Among the spinel oxides, ZnCo2O4 has been used as a potential candidate for various applications due to its beneficial structural and electronic properties. In the first work (Chapter 3), ZnCo2O4 flakes and spheres architecture along with inorganic salt as catalytic systems were developed, which exhibited excellent catalytic performance for the chemical fixation of CO2. Two mesoporous catalysts of ZnCo2O4 with different architecture, such as flakes (ZnCo-F) and spheres (ZnCo-S) were synthesized using the hydrothermal and reflux method, respectively. It utilized as a heterogeneous catalyst for cycloaddition reaction. The XRD, SEM and BET analyses were used to examine the chemical and textural property of the catalyst. The bifunctional property of catalysts is mainly attributed to strong acidic and basic properties confirmed by TPD (NH3 & CO2) analysis. ZnCo-F catalyst exhibited excellent conversion of propylene oxide (99.9 %) with good corresponding selectivity of propylene carbonate (≥ 99 %) in the presence of inorganic salt (KI) at 120 oC, 2 MPa, 3 h. In addition, ZnCo-F catalyst demonstrated good catalytic applicability towards the various substrates scope of the epoxide. The proposed catalyst exhibited good reusability for cycloaddition reaction without significant change in its catalytic activity. Ionic liquids have become prominent as catalysts due to their high catalytic activity, nonflammability, high thermal stability, ease of preparation, low cost, low vapour pressure, and environmental friendliness. In the next work (Chapter 4), the synthesis of 3-(2-hydroxyethyl)- 1-vinyl-1H-imidazol-3-ium chloride [EvimOH][Cl] and 3-(2-hydroxyethyl)-1-vinyl-1H-imidazol-3-ium sulphate [EvimOH][HSO4] ionic liquids were presented for cycloaddition reactions of CO2 and epoxides into cyclic carbonates. The synthesized ionic liquids were characterized by FT-IR, 1H- and 13C-NMR spectroscopic methods. Also, the physical properties of ionic liquids analyzed by TGA and DTA. Further, the CO2 consumption was studied by developing a binary catalytic system with bases such as DBU, TEA, DIPEA, piperidine, pyrrolidine, aniline. The developed binary ([EvimOH][Cl]/base) catalytic system exhibited the excellent catalytic activity of 99.8 % conversion and ≥ 99 % selectivity under mild reaction conditions without the aid of solvent and metal co-catalysts. Furthermore, the results show that the improved activity from the binary system is due to synergistic effect among −OH functional group from the cation, reactive acidic C(2)-H in the imidazolium ring and amine-containing bases, which promote the CO2 absorption. Also, a plausible mechanism of cyclic carbonate formation and kinetic study in the presence of a binary catalytic system was demonstrated. Substantially, biomass-based catalytic systems have attracted much attention because of their relatively low environmental effects. Carbonaceous materials have recently attracted much attention in heterogeneous catalyst synthesis due to their easy availability from natural sources, simple synthetic process, easy separation from the reaction mixture, good chemical and thermal stability. In the final work (Chapter 5), the utilization of glucose, oxalic acid and urea to derive carbonaceous materials were discussed for chemical fixation of CO2 with epoxides into cyclic carbonates without the aid of solvent. The derived heterogeneous carbonaceous materials containing different carboxyl, hydroxyl and amines were developed by facile and straightforward hydrothermal method and used with a certain amount of KI which acts as co-catalyst. The synthesized catalysts such as Glucose Carbonaceous Material (GCM), Oxalic-Glucose Carbonaceous Material (O-GCM) and Urea-Glucose Carbonaceous Material (U-GCM) were characterized by FTIR, XRD, TGA, BET, TPD, SEM and XPS analysis techniques. The results show that the catalyst has excellent catalytic performance under mild reaction conditions with outstanding stability owing to easy separation from the reaction mixture. Moreover, results demonstrate that the catalyst has shown superior catalytic activity due to the presence of amine (-NH), hydroxyl (-OH), and carboxylic (-COOH) enriched carbonaceous framework, which enables synergistic effect to enhance the catalytic performance considerably. 현재 빠르게 증가하는 이산화탄소 (CO2)의 대기 배출량을 제어해야 하는데 이 CO2는 탄소 함유 물질의 호기성 연소에서 생성된다. 화석 연료 연소를 통해 거대하게 생산되며 가장 주요한 온실 가스로 간주된다. 연도 가스로부터의 CO2 포집과 활용은 산업 연소 과정에서 온실 효과를 완화하기 위한 최선의 선택으로 간주되고 있다. 수년에 걸친 연구들은, 대기 CO2의 상당한 증가와 기후 변화 및 해양 산성화와 같은 잠재적인 환경 위험으로 인해 CO2를 고부가가치 화학 물질 및 공급 원료로 성공적으로 전환하는 데 집중되었다. 그러나 CO2 전환은 열역학적으로 안정적이고 동역학적으로 불활성이기 때문에 계속 연구가 필요하다. 적절한 촉매 시스템의 개발은 부분적으로이 문제를 극복하는 데 도움이 될 수 있다. 촉매는 화학 물질의 합성에 필요한 변형을 달성하는 데 성공적으로 사용된 중요한 도구로서 생산 비용을 줄이고 반응의 원자 경제를 향상시킬 수 있다. 이와 관련하여 생태학적, 경제적 관점에서 CO2의 화학적 고정을 위한 효과적이고 직접적인 촉매 시스템을 개발하는 것은 연구 의 중요한 과제이다. CO2를 다양한 고부가가치 제품으로 직접 전환하기 위해 자연적으로 풍부하고 저렴하며 환경 친화적이며 상업적으로 이용 가능한 전구체 물질로부터 효율적이고 직접적인 촉매 시스템 (금속 산화물, 이온 성 액체 및 탄소 계 촉매 시스템)을 구축하고자 하였다. CO2와 에폭사이드의 고리형 탄산염으로의 고리 화 첨가 반응은 배터리의 전해질, 극성 비양성 자성 용매, 폴리머 합성용 단량체, 중간체 제약 및 정밀 화학 산업과 같은 광범위한 응용 분야에 활용 가능하다. 전이 금속 산화물 (TMO)은 다양한 분야에서의 응용으로 인해 많은 연구자들의 관심을 끌고 있고 또한 루이스 산-염기 촉매로서 중요성이 크다. 스피넬 산화물 중 ZnCo2O4는 유리한 구조적 및 전자적 특성으로 인해 다양한 응용 분야의 잠재적 후보로 사용되었다. 3장에서는 촉매 시스템으로서 무기 염과 함께 ZnCo2O4 플레이크 및 구형 구조가 개발되었고 이는 CO2의 화학적 고정을 위한 우수한 촉매 성능을 나타 내었다. 플레이크 (ZnCo-F) 및 구형 (ZnCo-S)와 같이 구조가 다른 ZnCo2O4의 두 메조 포러스 촉매는, 각각 열수 및 환류법으로 합성되었다. 이는cycloaddition 반응을 위한 이종 촉매로 활용되었다. XRD, SEM 및 BET 분석은 촉매의 화학적 및 조직적 특성을 조사하는 데 사용되었다. 촉매의 이 기능적 특성은 주로 TPD (NH3 & CO2) 분석에 의해 확인된 강산성 및 염기성 특성에 기인한다. ZnCo-F 촉매는 120 oC, 2 MPa, 3 시간에서 무기염 (KI)의 존재 하에서 프로필렌 카보네이트의 우수한 선택성 (≥ 99 %)과 함께 프로필렌 옥사이드 (99.9 %)의 우수한 전환율을 나타내었다. 또한, ZnCo-F 촉매는 에폭사이드의 다양한 기질 범위에 대해 우수한 촉매 적용성이 확인되었다. 제안된 촉매는 촉매 활성에 큰 변화없이 고리화 첨가 반응에 대해 우수한 재사용성을 나타냈다. 이온성 액체는 높은 촉매 활성, 불연성, 높은 열 안정성, 제조 용이성, 저렴한 비용, 낮은 증기압 및 환경 친화성으로 인해 촉매로 강점이 있다. 4 장에서는 3-(2-hydroxyethyl)-1-vinyl-1H-imidazol-3-ium chloride [EvimOH] [Cl] 및 3-(2-hydroxyethyl)-1-vinyl의 합성 -1H-imidazol-3-ium sulphate [EvimOH] [HSO4] 이온 성 액체는 CO2와 에폭사이드의 고리형 탄산염으로의 고리 첨가 반응을 위해 제안되었다. 합성된 이온성 액체의 구조 및 물성은, FT-IR, 1H- 및 13C-NMR 분광법, TGA와 DTA로 분석되었다. 또한 DBU, TEA, DIPEA, 피페리딘, 피롤리딘, 아닐린과 같은 염기로 이원 촉매 시스템을 개발하여 CO2 반응에 적용하였다. 개발된 이원 ([EvimOH] [Cl] / 염기) 촉매 시스템은 용매 및 금속 조 촉매의 도움없이 온화한 반응 조건에서 99.8 % 전환율과 99 % 이상의 선택성의 우수한 촉매 활성을 나타내었다. 또한, 결과는 이원계로부터의 향상된 활성은 양이온의 -OH 작용기, 이미다졸륨 고리의 반응성 산성 C (2) -H 및 아민 함유 염기 사이의 상승 효과에 기인하여 CO2 흡수가 촉진시킴을 보여준다 . 또한, 이원 촉매 시스템의 존재 하에서 순환 탄산염 형성 및 운동학적 메커니즘이 제안되었다. 실질적으로 바이오 매스 기반 촉매 시스템은 상대적으로 낮은 환경 영향으로 인해 많은 관심을 끌었다. 탄소질 재료는 최근 천연 공급원으로부터의 용이한 가용성, 간단한 합성 공정, 반응 혼합물로부터의 용이한 분리, 우수한 화학적 및 열 안정성으로 인해 이종 촉매 합성에서 많은 관심을 받고 있다. 5 장에서는 탄소질 물질을 유도하기 위해 포도당, 옥살산 및 요소를 사용하여 용매를 사용하지 않고 에폭시드와 함께 이산화탄소를 고리형 탄산염으로 화학적으로 고정하는 방법을 조사하였다. 서로 다른 카르복실, 하이드록실 및 아민을 포함하는 파생된 이종 탄소질 물질은 쉽고 간단한 열 수법으로 개발되었으며, 조촉매 역할을하는 일정량의 KI와 함께 사용되었습니다. GCM (Glucose Carbonaceous Material), O-GCM (Oxalic-Glucose Carbonaceous Material) 및 U-GCM (Urea-Glucose Carbonaceous Material)과 같은 합성 촉매는 FTIR, XRD, TGA, BET, TPD, SEM 및 XPS 분석으로 특성화되었다. 촉매가 반응 혼합물로부터의 용이한 분리로 인해 우수한 안정성과 함께 온화한 반응 조건에서 우수한 촉매 성능을 가짐을 보여준다. 더욱이, 결과는 촉매가 아민 (-NH), 하이드 록실 (-OH) 및 카복실산 (-COOH)이 풍부한 탄소질 프레임 워크의 존재로 인해 우수한 촉매 활성을 보였으며, 이는 촉매 성능을 상당히 향상시키는 상승 효과를 가능하게 한다.

귀금속 함량 및 촉매 마일리지에 따른 삼원촉매 활성 예측을 위한 Reaction kinetics 개발 : Reaction Kinetics for Predicting Performance of Modern Three-Way Catalyst as a function of Noble Metal Loading and Catalyst Mileage

강성봉 포항공과대학교 일반대학원 2015 국내박사

Three-way catalyst (TWC) has been widely employed as the most efficient catalytic system to simultaneously remove all three major air pollutants including CO, HCs and NOx from the automotive exhaust gas, mainly those emitted from gasoline engine. Moreover, the modern commercial TWC consists of the bimetallic Pd/Rh catalyst, instead of the traditional Pt/Rh catalyst, due to economic interests. In addition, the washcoating methodology of current bimetallic Pd/Rh TWC monolith has shifted from the conventional single-layered catalytic system to the double-layered one to avoid the catalyst deactivation caused by the formation of Pd-Rh metal alloy upon thermal aging. The development of a kinetic model describing the alteration of the TWC performance with respect to the catalyst metal loading and time-on-stream has been a long-lasting task in automotive reaction engineering. Indeed, the acvive metal surface area (MSA) representing the number of active reaction sites formed on the catalyst surface plays a critical role in determining the TWC activity, and strongly depends on the catalyst noble metal loading and the degree of catalyst aging. A simple activity function concept based on the physicochemical characteristics including the MSA of novel metals may be one way for possibly predicting the TWC performance varied by both the noble metal loading and the catalyst mileage. In the present study, 3D activity functions for each Pd and Rh catalyst have been independently developed on the basis of the active metal surface area (MSA) of Pd or Rh, respectively, which can be used to predict the TWC performance as a function of Pd or Rh loadings and the catalyst mileage. To develop the activity function for the Pd catalyst, the commercial Pd-based TWCs (Pdc1) with a wide range of the Pd loading from 20 to 240 g/ft3 were obtained from GM R&D. Another series of commercial Pd-based TWCs (Pdc2) with the Pd loading from 140 to 280 g/ft3 were employed for broadening the applicability of the activity function developed in this study. In addition, a series of the model Pd TWCs (Pdm) with the Pd loading from 50 to 200 g/ft3 was prepared to further validate the activity function derived. Based upon the alteration of the Pd MSA examined by CO chemisorption, the 3D activity function for the Pd catalyst has been developed over the wide range of the Pd loadings from 20 to 280 g/ft3 and the catalyst mileage from 4k to 100k miles by integrating the second-order deactivation kinetics with the initial condition at 4k miles described as the activity function for 4k reference catalysts. The nonlinear catalytic activity of two series of commercial Pd-based TWCs (Pdc1 and Pdc2) as a function of the Pd loading and catalyst mileage was reasonably well predicted by the 3D activity function developed for the Pd catalyst. It has also proven to be universally applicable for the lab-prepared model Pdm catalysts with respect to the catalyst Pd loading and mileage. Moreover, the catalyst mileage of the Pdc3 catalyst aged by engine dynamometer was correctly estimated by the new 3D mileage function, which can be used in predicting the life expectancy of any Pd-based TWCs. The 3D activity function for the Rh catalyst on the basis of the alteration of the Rh MSA has been also developed by integrating the second-order deactivation kinetics. The activity function for the Rh catalyst again well predicted the linear dependence of the catalytic activity with the increasing Rh loading from 2.5 to 15 g/ft3 as well as the nonlinear decreasing trend of the catalytic activity with the increasing of the catalyst mileage from 4k to 100k miles. Based upon the detailed TWC reaction mechanism postulated, the reaction kinetics for each 4k Pd and 4k Rh catalysts employed as a reference catalytic system has been developed to predict the TWC performance of each Pd and Rh catalysts as a function of the Pd or Rh loading and the catalyst mileage. For the Pd catalyst, the overall reaction kinetic model combined with the activity function and the reference reaction kinetics reasonably well predicted the TWC performance of the commercial Pdc1 and Pdc2 and lab-prepared Pdm catalysts as a function of both the catalyst Pd loading from 20 to 280 g/ft3 and mileage from 4k to 100k miles. In addition, the TWC performance of the commercial Rh catalyst as a function of the Rh loading from 2.5 to 15 g/ft3 and the catalyst mileage from 4k to 100k miles was reasonably well described by the reaction kinetics combined with the activity function for the Rh catalyst. To develop the intrinsic reaction kinetics for double-layered bimetal Pd/Rh TWC monolith catalyst, the individual reaction kinetics derived for the Pd and Rh catalysts was combined with no further adjustment of the kinetic parameters obtained from individual Pd and Rh catalyst. The TWC performance of the lab-prepared double-layered Pd80/Rh2.5 monolith reactors was well captured by the combined reaction kinetics incorporated into the 2D non-isothermal monolith reactor model, regardless of the location of the catalysts washcoated. The combined kinetic model developed was also capable of predicting the TWC performance of the commercial double-layered Pd80/Rh2.5 monolith reactor (Rh on the top layer and Pd in the bottom layer). Consequently, the overall reaction kinetics for the double-layered Pd/Rh TWC monolith reactor as a function of the catalyst metal loadings and mileage has been derived by incorporating the activity functions developed for the Pd and Rh catalysts into the detailed reaction kinetics of the reference 4k Pdc1-240 and 4k Rh15 catalysts. The long-term catalytic performance (up to 100k miles) of the commercial Pdc1-80/Rh10 TWC monolith reactor as a function of the catalyst mileage was remarkably well described by the overall reaction kinetics combined with the individual reaction kinetics of the reference catalysts and their corresponding activity functions.

Syngas Production via Combined Steam and CO2 Reforming of Coke Oven Gas over Ca-Promoted Ni/MgAl2O4 Catalysts

Lee, Jin Hyang 고려대학교 대학원 2015 국내석사

The coke oven gas (COG) is a byproduct gas produced in the process of coal carbonization for the manufacture of metallurgical cokes used as reducing agents for the reduction of iron ore. Its main constituents are -- by volume of dried gas -- H2 (48-55%), CH4 (28-30%), CO (5-7%), N2 (1-3%), and CO2 (2-3%). COG has been mainly used as heat source to maintain the temperature of coke oven. In this study, CH4 contained in COG, CO2 collected and separated from the blast furnace gas (BFG) and H2O are used as reactants for the combined reforming process to produce syngas composed mainly of H2 and CO in order to take advantage of COG through the value-added reutilization of this byproduct gas. If this syngas is used as reducing gas for DRI manufacture, it will surely lead to the reduction of usage of coke as an alternative reducing agent; thus reducing the amount of CO2 emissions. Ni-based catalysts are commercially used for the hydrocarbon reforming due to their advantage of high catalytic activity and low cost, but they have problems of drastic deactivation due to coke deposition, sulfur poisoning, and sintering of catalyst particles at high temperatures. Hence, this study aimed to produce a reducing gas (H2/CO) through the combined H2O and CO2 reforming (CSCR) of COG and Ca was added as a promoter for the purpose of strengthening the Ni/MgAl2O4 catalyst in terms of coke resistance and sinter-stability. Ca-promoted Ni/MgAl2O4 catalysts with different Ca/Ni ratios of 0.0-1.0 were prepared by co-impregnation method for syngas production via CSCR of COG. The physicochemical properties of prepared catalysts were characterized by XRD, BET, H2-chemisorption, TPR and CO2-TPD. The SEM, TGA and TEM analysis was carried out to observe the coke deposition and agglomeration of Ni particle in used catalysts. It was confirmed that Ca addition improved the Ni dispersion, strong metal-support interaction (SMSI) and CO2 adsorption of catalyst. The CSCR of COG was carried out under the reaction conditions of CH4:H2O:CO2=1:1.2:0.4, 700 oC-900 oC, 5 atm. The Ca-promoted 10Ni/MgAl2O4 catalysts show higher CH4 conversion and coke resistance than 10Ni/MgAl2O4 catalyst without Ca addition. In particular, 10Ni-5Ca/MgAl2O4 catalyst with Ca/Ni ratio of 0.5 showed a good catalytic activity and sinter-stability in CSCR of COG at high temperature of 900 oC due to high Ni dispersion and improved SMSI.

Heterogeneous Catalysts in Chemical Conversion of Carbon dioxide

김대한 성균관대학교 일반대학원 2016 국내박사

Recently, carbon dioxide (CO2) has been regarded as a main reason of greenhouse effect, resulting in irreversible climate change of the Earth. Thus, catalytic conversion of CO2 using heterogeneous catalysts has been much attracted because CO2 can be a C1 building block for making valuable fuels and chemicals such as methanol and formic acid. Carbon dioxide reforming of methane (CRM) is one of the most promising CO2 utilization methods because one can simultaneously remove two greenhouse gases of methane (CH4) and CO2, and produce synthesis gas [carbon monoxide (CO) and hydrogen (H2)]. In general, nickel (Ni) has been widely used as a catalyst for the CRM reaction; however, it has been found that thermal aggregation of Ni particles induces low catalytic activity for the reaction at high temperature. Moreover, graphitic carbons (coke) generated during the CRM reaction block the active sites of Ni catalyst, resulting in gradual decrease of catalytic activity with reaction time. Thus, in this work, the regular- and inverse-structured Ni catalysts were prepared to improve the catalytic activity and stability of Ni for the CRM reaction. In order to prepare the regular-structured Ni catalyst, mesoporous silicon dioxide (SiO2) was used as a substrate and Ni was deposited on the substrate surface by atomic layer deposition (ALD) method. The SiO2-supported Ni catalyst showed outstanding activity and stability for the CRM reaction at 800 oC, as a result of confinement of Ni with a mean size of ~10 nm into the pores of SiO2. In addition, catalytic reactivity of the titanium dioxide (TiO2)-deposited inverse Ni catalysts was also evaluated for the CRM reaction at 800 oC. The TiO2 layer facilitated the formation of separate carbon filaments rather than coke on the Ni surface, reducing the possibility of the deposited carbon layers to cover and poison the Ni active sites of catalysts. Thus, the TiO2/Ni catalysts showed the enhanced catalytic stability for the reaction, although the initial performance of the catalysts was inferior to that of the bare Ni catalyst. Another CO2 conversion method suggested in this thesis is reverse water gas shift (RWGS) reaction which is one of the key processes of CO2 hydrogenation to form methanol using CO and H2 (CAMERE process). In this reaction, designing of new catalysts having outstanding activity and stability is a main concern. Therefore, the two different types of catalysts were suggested here and their catalytic activities for the RWGS reaction were evaluated at high temperature. One of them was a barium zirconate-based perovskite-type catalyst and the catalytic performance was analyzed with yttrium (Y), cerium (Ce) and Zn dopants for the RWGS reaction at 600 oC. It was found that the Y and Zn-doped BaZr0.8Y0.16Zn0.04O3 (BZYZ) catalyst had a superior activity for the RWGS reaction, while additional Ce doping on the BZYZ catalyst induced Zn-deficient surface sites and instability of chemical structure of the catalyst, resulting in decrease of catalytic activity. Unsupported iron (Fe)-oxide nanoparticle synthesized by simple wet-chemical process, and the catalytic ability of the catalyst for the RWGS reaction was evaluated at 600 oC. The Fe catalyst was resistant to thermal aggregation and coke accumulation on the catalyst surface, because the atomic carbon (C) and oxygen (O) formed on the catalyst surface were diffused into the bulk of Fe catalyst, preserving the chemical structure of the catalyst surface.

Catalyst design for CO-assisted NOx reduction using mechanistic and microkinetic modelling

Malik Waqar Arshad University of Science and Technology (UST), Korea 2022 국내박사

Amorphization and Exsolution of M-Doped CexTi1-xO2 (M=Zr, W, Mn) Catalysts andIts Carbon Nanostructure Reinforced Metal Oxides as Supports

조승현 부산대학교 대학원 2019 국내박사

Cerium oxide (CeO2, Ceria) is a substance used in various fields such as catalyst, fuel cell, coating, gas sensor and oxygen membrane, and is widely used as a main catalyst material as well as a promoting material for improving the efficiency of the catalyst system. The CeO2 has fluorite cubic structure (Fm-3m). The cerium ion located at the corner of the cubic has 8 equivalent nearest neighbor oxygen and the oxygen ion is located at the center of the tetrahedral site where the cation is formed. This structure has a large vacant octahedral hole in a structure, facilitating the hopping movement of oxygen ions in the lattice. The lattice oxygen can be reversibly removed depending on the temperature and oxygen partial pressure conditions of the reaction environment. It has the feature to save. Due to this oxygen storage capacity (OSC) which can improve the efficiency of the oxidation and reduction reaction, CeO2 has been actively studied as a catalyst for promoting the activity of the transition metal oxide catalyst. Based on the richest reserves within rare-earth materials, recent studies of CeO2-based catalysts as the main-catalyst for replacing precious metal catalysts are actively underway. To maximize the OSC of CeO2, solid solution formation, nanostructure production, and amorphization research were the essential factors. However, when thermally unstable CeO2 is used in the form of nanoparticles, there is a serious problem that the activity of the catalyst is lowered in the use environment due to rapid grain growth and aggregation. To overcome these limitations, exsolution and intelligent (re-generative) catalysts are developed. It is the a method to form nano-particles on the surface through reduction heat treatment after doping target elements in the matrix such as perovskite. The synthesized catalyst is characterized by excellent grain growth resistance at high temperature due to chemical bonding of the precipitated nanoparticles and the matrix on the surface. The present exsolution phenomenon is selectively observed only in a limited number of matrix. On the other hand, observation of exsolution in amorphous matrix has not been reported. The precipitation of CeO2 on the amorphous phase matrix can induce simultaneous reaction between the nanoparticle catalyst and the amorphous catalyst exposed on the surface. The amorphous phase not only has a higher specific surface area than the crystalline phase but also has a liquid-like surface structure. The catalytic performance can be maximized by the high concentration of surface imperfection site. However, due to the lack of crystallinity, which means a long-range order, there is a limit to analyzing the material characteristics by the diffraction and transmission electron method which are commonly used. In this study, an amorphous catalyst was synthesized by using Ce-Ti oxide and the process of manufacturing nano-sized CeO2 on the surface was designed. The amorphous Ce-Ti oxide catalysts were prepared using the sol-gel method and were confirmed to be amorphous phase without crystallization by TEM analysis. X-ray absorption spectroscopy was performed as a representative (bulk) analysis throughout the specimen and the Ce-Ce bonds corresponding to the long-range order were decreased. In the case of the catalyst synthesized through the exsolution process, most of the samples were uniformly precipitated with CeO2 of ~ 5 nm on the surface while maintaining the amorphous phase matrix. In the fixed-bed reactor measurement for nitrogen oxide removal efficiency, the highest removal efficiency of nitrogen oxide was obtained at C3T7 composition in which nano-sized CeO2 was deposited most uniformly on the surface of amorphous matrix. The irregular octahedral CeO2 formation was observed In TEM tilting analysis. In conclusion, this unique precipitation of CeO2 exposes crystal planes which had high efficiency for SCR reaction. We judged that the expression of exsolution in the Ce-Ti amorphous matrix and confirmation of the enhancement of the efficiency were the first study of linkage between amorphous or nano-sized catalyst. In addition, to improve the mechanical properties of the catalyst support, carbon nanostructure was grown inside TiO2 using nano size Ni catalyst. According to the growth of CNT, not only the 3-point bending strength but also the compressive strength measured by commercial support showed ~ 12% improvement. These results suggest that the improvement of the strength can be expected through simple impregnation of the Ni sol with the commercial support, and it can be a solution to the problem of support fracture by LPA and vibration.

Pt/TiO2 촉매의 특성이 CO 상온 산화 반응에 미치는 영향 연구

김거종 경기대학교 일반대학원 2013 국내석사

오늘날 현대인들은 90% 이상을 실내공간에서 생활하게 되면서 생활, 주거, 근로, 작업공간의 쾌적한 환경조건에 대한 요구가 증가되고 있다. 특히, 겨울날 실내의 난방을 위한 보일러 및 작업공간에서 발생되는 일산화탄소에 의해 가스 중독사고가 다량 발생하고 있는 실정이다. 이러한 일산화탄소 제거 기술로는 환기 및 필터링, 제습, 선태식물, 촉매 등의 방법이 있지만, 다양한 문제점으로 인하여 상기 방법 중 촉매를 이용하는 방법이 가장 각광받고 있다. 하지만 촉매를 이용하는 방법 역시 상온의 온도에서는 낮은 전환율의 문제점을 가지고 있으며 촉매의 deactivation 문제를 가지고 있어, 이에 대한 연구가 필요한 실정이다. 이에 본 연구에서는 실내공간에서 존재하는 일산화탄소를 제거하기 위해 상온에서 별도의 에너지원 없이 일산화탄소를 제거 할 수 있는 촉매를 연구함에 그 목적이 있다. 본 연구에서는 산화촉매에 널리 사용되는 대표적 활성 물질인 Pt를 사용하였고 지지체로는 상용 촉매로 많이 사용되어지며, 그 물리적 특성이 기타 물질에 비해 일정한 anatase-TiO2를 사용하여 Pt/TiO2 촉매의 CO 상온 산화 반응특성 연구를 수행하였다. Pt/TiO2 촉매의 경우 촉매제조공정인 환원온도에 따라 촉매의 활성금속인 Pt의 valence state가 변하게 되고 Pt0의 비율이 높을 때 우수한 CO 상온 산화 반응을 보였다. Pt/TiO2 촉매의 물리적 특성이 CO 상온 산화 반응에 미치는 영향을 조사하기 위해 다양한 상용 TiO2를 이용하여 각기 다른 물리적인 특성을 가지는 Pt/TiO2 촉매를 제조한 후 비교 평가한 결과 metal dispersion이 우수하고, active particle diameter가 작게 형성되는 Pt/TiO2 촉매가 CO 상온 산화 반응에 유리함을 확인 할 수 있었다. 또한, Pt valence state와 물리적 특성이 차이가 적은 Pt/TiO2와 Pt/Al2O3 촉매의 비교 실험을 통해 촉매의 환원성에 따라 촉매의 산소전달능력의 차이를 확인하였으며, 이로 인해 산소전달능력이 우수한 TiO2가 CO 상온 산화 반응에 우수함을 확인하였다. 마지막으로 Pt/TiO2 촉매들의 CO 상온 산화 반응 결과와 촉매의 표면 분석을 비교함으로써 본 연구에서 제조한 Pt/TiO2 촉매의 CO 상온 산화 반응 mechanism을 도출하였으며, CO 상온 산화 반응의 진행에 따라 변화되는 촉매의 표면을 분석하여 촉매의 deactivation에 대한 원인규명 및 deactivation model을 제안하였다. Since the rapid economic growth of the 1970s, the demand for comfortable, healthy living spaces has increased due to improve quality of life. As modern life is now mostly spent indoors, requirement for clean air in living, residence and work environment to gradually increase. However, the removal of harmful materials is emerging as a mahor task. Especially, the carbon monoxide generated by boilers for heating indoor and the workspace caused gas poisoning in cold day. Therefore, this study prepared Pt/TiO2 catalyst for the removal of carbon monoxide at room temperature. this study investigated of calcined catalyst after platinum loading on various TiO2 supports was very low. However It can be increase the activity at room temperature by reduction process. Pt/TiO2 catalyst activity is affected by the valence state of the Pt in carbon monoxide reaction. the valence state of Pt was controlled by reduction temperature. The catalyst pretreated reduction temperature at 600℃ was high activity in room temperature reaction. In this study, 8 anatase-type and 1 rutile TiO2 supports with various physical properties were selected to examine the effects of the Pt/TiO2 catalyst physical properties on catalytic activity. As a result, with increasing dispersion and decreasing active particle diameter, the catalyst activity was increased at room temperature. In addition, compared the activities of Pt/TiO2 and Pt/Al2O3 catalysts with all the same conditions in order to examine the effect the reducible support. As a result, Pt/TiO2 catalyst showed higher activity than the Pt/Al2O3 catalyst. The reason why Pt/TiO2 catalyst had a more excellent oxygen mobility than Pt/Al2O3 catalyst. Finally, in this study, this study suggests the mechanism of carbon monoxide and deactivation mechanism using Pt/TiO2 catalyst at room temperature by the analysis of the catalyst surface.

Study of supported Palladium and Platinum based catalysts for combustion of SOFC stack flue gas : SOFC 스택 배가스의 연소촉매 시스템 개발

호쿠아리플 영남대학교 대학원 2012 국내석사

Catalytic combustion of the flue gas from SOFC stack fueled by steam-methane reformer was studied by measuring the conversion versus temperature and on-stream operation hours in the tubular reactor and by characterizing the fresh and used catalysts. Pd-Pt bimetallic as well as monometallic Pd and Pt catalysts with different compositions were evaluated to study the catalyst activity and stability for combustion of SOFC stack flue gas. Catalysts containing palladium and platinum wash-coated on ceramic monolith were used to combust the stack flue gas consisting of methane, hydrogen, carbon monoxide, carbon dioxide, air and water vapor or nitrogen at various GHSV under the atmospheric pressure. H2 and CO were readily combusted under 200oC and CH4 was combusted above 300oC and catalyst activity was evaluated by measuring the conversion of combustibles as a function of temperature for all catalysts. The profile of methane conversion shifted toward lower temperature as the space velocity of stack flue gas flow decreased or the stack flue gas was diluted with nitrogen. As water vapor was included in the feed, the profile of methane conversion shifted toward higher temperature, indicating the inhibition by interaction of water vapor with catalyst active sites. Water vapor in the feed also affected catalyst stability adversely at low temperature and for the higher amount of water vapor. The catalyst deactivation could be reversed by raising the temperature or replacing the water vapor with nitrogen in the feed. Compared with the platinum-rich catalyst, the palladium-rich catalyst exhibited better activity and stability. Also, Pd-Pt composition was attributed as the synergistic factor of active metal ingredients affecting the catalyst activity and stability. The superiority of the palladium-rich catalyst could be explained by its relative abundance of active sites and its resistance to deactivation at elevated temperature. 본 연구에서는 메탄 수증기 개질에 의해 얻어진 연료를 기반으로 가동되는 고체산화물 연료전지(SOFC, solid oxide fuel cell)의 배기가스를 연소하기 위한 Pt-Pd계 연소촉매의 반응특성에 관한 연구가 수행되었다. 특히, Pt와 Pd 단독 또는 두 성분의 함량비에 따라 수소, 일산화탄소, 그리고 메탄과 같은 연소성 화합물의 촉매 연소반응 실험이 수행되었는데, 반응온도와 공간속도에 따른 촉매활성이 조사되었다. 수소와 일산화탄소는 200 ℃이하에서 촉매상에서 완전히 연소되었으며, 수소는 상온에서 완전 연소되는 것으로 확인되었다. 그러나 메탄의 경우에는 300 ℃이상에서 연소반응이 일어나며, 450 ℃이상에서 완전히 연소되는 것으로 나타났다. 이와 같은 완전연소 온도는 연료전지 배기가스의 조성에 따라 차이가 있는 것으로 나타났으며, 질소로 희석된 연소가스의 경우에 촉매연소온도가 낮아지는 경향을 나타내었다. 그러나 수분함량이 증가할 경우에는 오히려 촉매연소온도가 높아지는 경향을 나타내었다. 연료전지 배기가스에 함유된 수분의 함량이 높을 경우, 500 ℃이하의 온도에서는 촉매 비활성화가 동반되었다. 이와 같은 경향은 반응온도를 600 ℃이상으로 상승시켰을 경우, 촉매활성이 회복되므로 수분의 흡착에 의한 촉매활성저하로 판단된다. 이와 같은 특성은 촉매의 주 활성 성분인 Pt와 Pd의 혼합비에 따라서 달라지는데, Pd가 풍부한 이중금속 촉매상에서 촉매의 안정성이 높은 것으로 확인되었다. 한편, 공간속도의 증가에 의해서 촉매의 활성이 낮아지는 경향을 나타내었는데, 공간속도가 8000 h-1이하의 조건에서 높은 촉매활성을 가지는 것으로 조사되었다.

폴리설폰산 중심 촉매의 합성 및 촉매 에스테르화에 대한 응용 연구

강염휘 우석대학교 일반대학원 2021 국내박사

지방산은 매우 필수적인 원료이자 합성 중간체로 화장품의 합성, 식품첨가물, 계면활성제, 방부제 및 항진균제, 의약품 등의 각 분야에 서 널리 사용되고 있다. 산업적으로 지방산 에스테르의 제조는 주로 황산, 인산, p-톨루엔설폰산 및 일련의 유기 또는 무기 강산에 의해 촉 매되는 에스테르화 반응을 기반으로 한다. 그러나 이 촉매는 사용 과 정에서 설비 부식이 심하고 부반응이 많을 뿐 아니라 후처리가 복잡 하고 환경오염이 심하며 회수율이 낮은 점 등의 단점이 존재한다. 친 환경적, 효율성, 회수하기 쉬운 촉매 시스템을 발전시키는 것이 강력 한 대안이다. 본 연구에서는 β-사이클로덱스트린(β-CD)설폰산과 이온 액체(ILs)를 포함한 폴리설폰산 촉매를 조절 가능한 신세대 친환경 촉 매로서 설계 및 합성하였다. 이를 통하여 촉매의 산도가 향상되고 촉 매 성능도 개선되었다는 점은 주목할 가치가 있다. 그 결과로서 우선, 일종의 이온 교환법으로 6-O-설포부틸-β-사이클로덱스트린(SB-CD)을 제조하여 에스테르화 반응에 사용하였다. 제어변수법을 사용함으로써 촉매가 에스테르화 반응에 미치는 영향을 조사하고 반응 조건을 최적 화하였다. 본 촉매는 우수한 촉매 활성을 나타내었고, 해당 에스테르 로의 전환율이 90% 이상이었다. 두번째로, 4 종의 삼중심 술폰산 기능 화 이온 액체를 합성하고 이를 촉매로 사용하여 고급지방산 촉매합성 바이오 디젤에 적용하고 촉매의 성능에 미치는 영향을 세부적으로 살 펴보았다. 촉매 [DHDTMPS][Tos]은 5 번 재사용할 수 있었으며 실온에 서 제품을 촉매 시스템에서 분리할 수 있었다. 마지막으로, 6 종의 다 중심 술폰산 기능화 이온 액체를 합성하여 촉매 구조, 촉매 농도, 알 키드 비율, 반응 기질이 에스테르화에 미치는 영향을 관찰하였다. 이 중, 촉매 PEI 10000-N-C16 은 최적의 반응 조건에서 메틸올레이트(Methyl Oleate)의 생산량이 94.6%에 이르렀다. 촉매 PEI10000-N- C16 은 탄소 사 슬 길이가 다른 지방산의 적용 가능성이 높았다. Fatty acid esters are a kind of essential raw materials and synthetic intermediates, which are widely used in cosmetics synthesis, food additives, surfactants, anti-corrosion and anti-mildew agents and pharmaceuticals. Industrially, the manufacture of fatty acid esters are mainly based on esterification reaction catalyzed by sulfuric acid, phosphoric acid, p-toluenesulfonic acid and a series of organic or inorganic strong acids. Correspondingly, there are some disadvantages with using such catalysts, such as serious equipment corrosion, side reactions, complex post-treatment, serious environmental pollution, low recovery rate and so on. The development of green, efficient and easy to recycle catalytic systems is a powerful alternative. In this study, polysulfonic acid center catalysts including β-cyclodextrin (β-CD) sulfonic acid and ionic liquids (ILs), as new generation of green environmental-friendly catalysts with adjustable structure, were designed and synthesized. As a result, the acidity of the catalysts was enhanced, and the catalytic performance was improved as well. Firstly, the catalyst of 6-O-sulfobutyl-β-cyclodextrin (SB-CD) was prepared by one-step ion exchange method and applied to esterification reaction. The influence of catalyst on esterification was investigated by using the control variable method and the reaction conditions were optimized. The catalyst showed good catalytic activity, and the conversion of corresponding ester was more than 90%. Secondly, four kinds of tricentric sulfonic acid functionalized ILs were synthesized and used to catalyze the synthesis of fatty acid methyl ester using higher fatty acids. The effect of catalyst performance was investigated in detail. The catalyst [DHDTMPS][Tos] could be reused five times and the product could be separated from the catalyst system at room temperature. Lastly, six kinds of polycentric sulfonic acid functionalized ILs were synthesized, and the effects of catalyst structure, catalyst concentration, the ratio of alcohol to acid and reaction substrate on esterification were investigated. Under optimal reaction conditions, PEI10000-N-C16 has good catalytic activity and the yield of methyl oleate was 94.6%. PEI10000-N-C16 has good applicability of fatty acids with different carbon chain length.