Nail Yasyerli

The Catalytic Performance of Sol-Gel Alumina Supported Ti-Ce Catalysts for H2S Selective Oxidation to Elemental Sulfur

Abstract In this study, alumina supported Ti-Ce catalysts (10 % by weight and Ti/Ce molar ratio is 4:1) were prepared by using wet impregnation method and their catalytic activities were tested in H2S selective oxidation to elemental sulfur. The support alumina was synthesized by classical (SGC) and modified (SGM) sol-gel methods. The N2 adsorption-desorption, XRD, XPS, EDS and FTIR techniques were used to characterize the synthesized catalysts. The N2 adsorption-desorption isotherms showed that both catalysts have mesoporous structure. Only γ-Al2O3 crystalline phase together with amorphous structure were observed in the XRD patterns. The pyridine adsorbed FTIR analyzes showed that 10 %Ti-Ce@SGC and 10 %Ti-Ce@SGM catalysts have the same Lewis acidity. The activity tests were carried out at 250 °C and with a stoichiometric feed ratio of O2 to H2S being 0.5 for two different reaction times as 150 and 510 min. Complete conversion of H2S was obtained during 180 min. and 330 min. of reaction time over 10 %Ti-Ce@SGC and 10 %Ti-Ce@SGM, respectively. However, all catalysts showed very high sulfur selectivity. Sulfur deposition was detected over 10 %Ti-Ce@SGC catalyst both 150 and 510 min. of reaction time while it was observed after 510 min. of durability test over 10 %Ti-Ce@SGM catalyst. This can be the reason for the earlier loss of catalytic activity 10 %Ti-Ce@SGC than 10 %Ti-Ce@SGM.

H2S’ÜN SEÇİCİ KATALİTİK OKSİDASYONU İLE ELEMENTEL KÜKÜRT ELDESİNDE Ce-O KATALİZÖRLERİ

DOI: Bu çalışmada, modifiye edilmiş kompleksleştirme yöntemi ile Ce-O katalizörleri hazırlanmış ve seçici katalitik oksidasyon ile elementel kükürt eldesindeki aktiviteleri araştırılmıştır. Katalizör sentezinin son basamağı olan kalsinasyon işlemi farklı sıcaklıklarda (300oC, 350oC, 400oC ve 450oC) gerçekleştirilerek kalsinasyon sıcaklığının katalitik aktiviteye etkisi incelenmiştir. Hazırlanan katalizörlerle aktivite testleri 250°C sıcaklık ve farklı O2/H2S oranlarında sabit-yatak reaktör sisteminde gerçekleştirilmiştir. Farklı sıcaklıklarda kalsine edilen bütün katalizörlerin XRD desenlerinde yığın fazın “cerianite” kristal yapısında ve stokiyometrik olmayan oranda O2 bulundurduğu (CeO2-x) gözlenmiştir. Ce-O katalizörlerinin XPS analizi bu sonucu desteklemiş, katalizör yüzeyinde seryumun çoğunlukla +4 ve beraberinde +3 değerlikte bulunduğunu göstermiştir. Bütün Ce-O katalizörleri ile oldukça yüksek elementel kükürt seçiciliği (≥%97) elde edilmiştir. Bununla beraber, H2S seçici oksidasyonunda en uzun süre aktiviteyi (%69 H2S dönüşümü) 350oC’da kalsine edilen Ce-O–350 katalizörü göstermiştir. Katalizörlerin kalsinasyon sıcaklığının düşmesi katalitik aktivitede yükselme ile sonuçlanmıştır. Kalsinasyon sıcaklığının düşmesi Ce-O katalizöründe oksijen hareketliliğini olumlu etkileyerek daha uzun süre katalitik aktivite göstermesine neden olmuştur. 10.17341/gazimmfd.337632

FTIR Studies of Urea Decomposition over Pt-Alumina and Cu-Alumina Catalysts

Urea, as an ammonia source, has been known to be a highly selective and efficient reducing agent to remove NOx from the automobile exhaust gases. Transition metals, such as Pt, Pd, Ag and Cu, on alumina are active and stable for the reduction of NOx by urea. In this study, urea decomposition was investigated over a 1% Cu and 2% Pt on alumina catalysts prepared by a single step sol-gel technique. Urea decomposition over these catalysts was studied in helium atmosphere in the range of 100-400°C by using FTIR. The analysis of FTIR spectra gave information about NH3, NH4+, CO2 and isocyanate (CNO-) formation on 1% Cu/Al2O3 and 2% Pt/Al2O3 catalysts. OH and CH stretching vibration bands were also observed over these catalysts. Isocyanate peak was observed at 150°C on 2% Pt/Al2O3 catalyst. The corresponding peak was observed at 250°C on 1% Cu/Al2O3 catalyst. The peak corresponding to melamine was observed on 2% Pt/Al2O3 at all the temperatures except for 150°C. However, melamine peak was only detected on 1%Cu/Al2O3 at 150°C for two and four minutes. Reducing agents for NOx reduction were obtained over 1% Cu/Al2O3 catalyst at high temperatures and over 2% Pt/Al2O3 catalyst at low temperatures. It is concluded that the catalysts prepared using the sol-gel process are effective in the decomposition of urea as ammonia and isocyanate sources.

DYNAMIC ANALYSIS OF SORPTION OF VOLATILE ORGANIC COMPOUNDS IN WATER

Chlorinated and brominated volatile organic compounds are among the groundwater pollutants creating major environmental problems. In this study, dynamic behavior of certain volatile organic compounds in water was investigated by using a novel moment technique. Adsorption equilibrium constant and the penetration length of tracers were evaluated by the first absolute and the second central moment expressions derived for a pulse-response system. In order to obtain adsorption equilibrium constant and penetration length, pulse-response experiments were carried out with different tracers in a one-sided adsorption cell at 30°C. The adsorption equilibrium constants at the gas-water interface were calculated for 1,2-dichloroethane, 1,1,1-trichloroethane, and carbon tetrachloride. This study showed that the adsorption equilibrium constant and the penetration length values could be successfully evaluated using the one-sided adsorption cell moment technique. The adsorption equilibrium constant for 1,2-dichloroethane, 1,1,1-trichloroethane, and carbon tetrachloride were found to be 0.30, 0.49, and 0.54 cm3/cm2, respectively.