Production of porous heterogeneous support catalysts used in catalytic filtration of harmful gases and investigation of their catalytic activities

The air-fuel mixture is burned and released into atmosphere by internal combustion engines and other combustion engines found in industrial sites. All motor vehicles and industrial chimneys produce exhaust emissions. The fuels used to run vehicles, which have many different hydrocarbon contents, are very harmful to human health and the environment. The damage caused by the gas coming out of the exhausts to the environment is considerable. If these toxic gases originating from flue gases and motor vehicles are not filtered, the damage they cause to the atmosphere is very high. Catalytic converters are used to convert these gases, which are very harmful to nature and human health, into harmless ones. In this study, in the first stage, porous and high surface area interlayer materials were obtained on commercially obtained cordierite (SiO2.Al2O3.MgO) support material in the form of ceramic honeycomb with low thermal expansion coefficient. Additionally, powdered cordierite material was synthesized. Compounds with high surface area were obtained by applying an wachcoating process on these powder materials. The support materials were activated by treating them with HCl before doppin the interlayer materials to the powder and monolith cordierite surface, increasing the pore sizes of the surfaces. Yttrium (Y) and lanthanum (La) compounds, together with cerium compound (Ce), which has a high oxygen retention capacity, were added to the cordierite support materials at approximately 5% rates. In order to observe the positive or negative effects of the washcoating on the catalytic activities, yttrium (Y) and lanthanum (La) were coated on the support material in certain ratios (Y: La, 1:1). In addition, in this study, zircon (Zr) compound was coated on the support material at a ratio of Ce:Zr 1:1, as it is refractory, hard and resistant to chemical attacks, along with cerium compound (CZ). Catalytic activity studies were carried out by adding Pd, Pt and Ru elements at rates of ~1% and Rh element at rates of ~0.5 on coated support materials by impregnation method. In addition, sand sample (DK), which is in its natural form and contains high amounts of SiO2, TiO2 and ZrO2, was studied. The DK coded sample was coated with ~1% Pd after acid surface activation with HCl and its catalytic activity was measured. It was observed that the DK sample had a high CO→CO2 conversion of 98.78% without any coating process. This product, prepared as a catalyst, can be an alternative to products based on high-cost and time-consuming intermediate coatings for the filtration of harmful gases. In order to measure the effect of the Ce washcoating on the catalytic activity, the cordierite monolith compound was doped with ~1% Pd in its pure form (uncoated) (Cor-Pd). In the catalytic conversion studies conducted with Pd, it was observed that all interlayer compounds (Ce:La:Y:Zr- C-Cor:L-Cor:Y-Cor:Z-Cor) added to the cordierite monolith had high CO→CO2 conversion (> 99.00%). It has been observed that the cordierite monolith compound (Cor-Pd) without intermediate coating has a low catalytic effect and low CO→CO2 conversion (82.12%), as expected. When the catalytic activity of the synthesized powdered cordierite sample (pCor-Pd) coated with ~1 Pd was examined, high CO→CO2 conversion was observed (99.01%). Among the hybrid coating techniques, the sample coded CZ showed the highest catalytic activity in the study (99.81%). Among the hybrid coating techniques, the sample coded YL showed the lowest catalytic activity in the study (72.82%). Pd and Rh metal doped monoliths were used for catalytic conversion studies of NOx gas. Rhodium and palladium are noble metals used in catalytic converters to promote NOx conversion. Rhodium is known for its high NOx conversion efficiency at high temperatures, while palladium is known to be more effective at low temperatures. Catalytic activity studies were carried out by coating ~0.5% of Rh metal on monolith cordierite (C-Cor/Rh). In our study, it was observed that the Rh catalyst compound converted almost all (99.96%) of the harmful NO gas. It has been observed that the monolith compound (C-Cor/Pd) with ~1% Pd converts almost all (99.94%) of the harmful NO gas. It has been observed that both catalysts have high efficiency in harmful NOx gas conversion. In addition to the advantages of rhodium metal having high efficiency in the conversion of both CO→CO2 and NOx→N2 gases, its rarity in nature and its reputation as a high-cost metal due to this feature have limited the use of Rh as a catalytic converter. Due to this limitation of rhodium, future studies have shown that effective and more cost-effective catalysts can be obtained by hybrid doping of other precious metals or transition metals with catalyst properties, along with reduced amount of Rh on the support material. In this study, aqueous phase reforming (APR) technique was also studied to obtain H2 gas from glucose with Pt-doped cordierite monolith compound. Approximately 45 mL of gas was obtained from 4000 ppm glucose solution and it was observed that approximately 20% of this gas was H2. Additionally, the electrocatalyst properties of the compounds synthesized in this study were examined. The oxygen evolution reaction (OER) and hydrogen reduction reaction (HER) of each of the Pd-Pt-Rh-Ru catalysts of the cerium-zirconia intercoated monolith cordierite compound (CZ-Cor) were carried out in the electrochemical cell in 1.0 M KOH at a scanning speed of 50 mV s-1 at room temperature. It was observed that all prepared electrodes (CZ-Pd, CZ-Pt, CZ-Ru and CZ-Rh) were catalytically active in both (HER, OER) reactions. When the cyclic voltammetry (CV) and linear scanning voltammetry (LSV) polarization curves of the electrocatalysts were evaluated, it was observed that the Pt catalyst was the most effective catalyst for both HER and OER. As a result of the experiments, the electrocatalyst activity order for both H2 reduction and oxygen evolution studies was determined as Pt>Pd>Rh>Control>Ru. In the later stages of the study, catalytic conversion studies were carried out by reducing the weight ratios of high-cost precious metals on the cordierite monolith compound and loading more economical metals such as Ni and Cu, and it was highly effective catalytic conversion with compounds with Pd (C-Cor/NiPd and C-Cor/Cu/Pd) reduced by 75% compared to the C-Cor/Pd compound. In the later stages of our study, cerium-coated TiO2 and ilmenite (FeTiO3) compounds were synthesized as an alternative to the cordierite compound, and catalytic conversion studies of these compounds and aqueous phase reforming were carried out to obtain hydrogen gas and methane gas from bio-renewable sources. It has been observed that both compounds have very high CO→CO2 conversion and are suitable methods to be developed for the production of H2:CH4 gases from biomass. This study has shown that innovative, cost-effective and highly efficient catalytic converters can be obtained by shaping the quality and quantity of the precious metals to be dopped to the support material through effective washcoating modelling. Apart from the cordierite monolith compound, it has been observed that the catalysts prepared from SiO2-based natural geological samples, which contain metals such as zircon with high thermal resistance and metals such as cerium and lanthanum with oxygen retention capacity, without being subjected to time-consuming and costly intermediate coating processes, have highly efficient catalytic conversion. In line with these data, it is thought that these geologically based materials will shed light on researchers in terms of their routine use in relatively larger, costly applications that require more raw materials (factory chimneys, etc.) compared to monoliths. In addition, it was determined that the compounds obtained in the study were suitable for the aqueous phase reforming (APR) technique to obtain H2 gas and/or methane gas (CH4) from organic substances. It is thought that improving the structures of the catalysts will provide researchers with a different perspective for obtaining H2 gas, which is thought to be the energy source of the near future. It is thought that obtaining innovative solid-supported washcoated catalysts and electrodes for H2 gas production applications from electrolysis will arouse interest in this type of catalysts among researchers in the near future.