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Öğe Activity and stability of TiO2 samples with different phase compositions in the decomposition of formaldehyde in SCW(ELSEVİER, 6 January 2021) Ateş, AytenTiO2 samples with different crystal sizes and compositions were synthesized using a sol-gel method at different calcination temperatures (350–900 °C). The activity and stability of TiO2 samples were determined by the gasification of formaldehyde in supercritical water (SCW) and by treatment in SCW. Increasing calcination temperature and SCW gasification (SCWG)/SCW treatment decreased the surface area of anatase TiO2 samples due to growing crystallite size via agglomeration and sintering. Among anatase TiO2 samples, the TiO2 calcinated at 450 °C was found as the most suitable material under SCW conditions. However, the surface area of rutile TiO2 slightly increased from 17.2 m2 g−1 to 19.8 m2 g−1 with the weakly crumbling of particles during SCWG. The highest hydrogen formation (63%) from formaldehyde in the SCW was obtained in the presence of anatase TiO2 calcined at 350 °C and rutile TiO2 calcined at 800 °C. CO2 formation in the presence of anatase TiO2 is higher than rutile TiO2 because of the presence of active lattice oxygen species (O−, O2−) based on O2-TPD.Öğe Aromatik Karışımların Hidrodealkilasyonuna Katalizör Modifikasyonun Etkisi(Gazi Üniversitesi, 2022) Ateş, Ayten; Yeniova, Hasip; Alibeyli, RafigPromoter ile modifiye edilmiş Cr-Al2O3 yüzeyinde mezitilenin benzen, toluen ve ksilene hidrodealkilasyonu n-dekanın varlığında çalışılmıştır. Cr-Al2O3 katalizörünün aktivitesine ve stabilitesine, reaksiyon sıcaklığının, WHSV, krom impregnasyonunun tür ve miktarı ve V, Cs, Ni ve Mo gibi promoterların etkisi incelenmiştir. N-dekanın mezitilene eklenmesi, metil ve etil radikallerinin ortamda bulunmasıyla, Cr-Al2O3 katalizörünün hidrodealkilasyon aktivitesini artırdı. V ve Cs ile modifiye edilmiş katalizör (V-Cs-Cr-Al2O3), stabilite, ürün seçiciliği ve girdi dönüşümü için ticari Pyrotol (Houdry, USA) katalizörü ile karşılaştırılabilir performans gösterdi.Öğe Demir içeren ZSM-5 tipi zeolitler yüzeyinde propanın oksidatif dehidrojenasyonu(2010) Ateş, Ayten; Hardacre, Chris; Goguet, Alexandre; Bteıtkopf, Cornelia[Abstract Not Available]Öğe Doğal ve Modifiye Edilmiş Sepiyolit ile Sulu Çözeltilerden Arsenik ve Manganın Adsorpsiyonu ile Ayrımı(2019) Ateş, Ayten; Yaşar, GökhanDoğal sepiyolit kil minerali Türkiye’nin Maden Tetkik ve Arama (MTA) kurumundan sağlanmış ve 2.5 M NaOH ile modifiye edilmiştir. Doğal (SP) ve modifiye edilmiş sepiyolit (Na-SP) örnekleri XRD, N2 adsorpsiyonu-desorpsiyonu, FTIR, SEM-EDS ve NH3-TPD ile karakterize edilmiştir. NaOH ile sepiyolitin modifikasyonu, sepiyolitin önemli miktarda desilikasyonuna ve dekatyonizasyonuna neden olmuştur. Sepiyolitin alkali muamelesi ile silisyum ve magnezyum çözünmesi sonucu sepiyolitin ortalama gözenek çapında artış ve yüzey alanında 187. 8 m2 g -1 ’den 7.1 m2g -1 ‘a azalma belirlenmiştir. Ayrıca, zayıf ve orta asit merkezleri azalırken, güçlü asit merkezleri artmıştır. SP ile maksimum As(III) ve As(V) ayrımı pH=1.5’de sağlanmış olup, değerler yaklaşık olarak sıra ile 8.9 mg g-1 ve 26.8 mg g-1 ’dır. Na-SP örneklerinde maksimum As(III) ve As(V) ayrımı pH=5.0’de sağlanmış olup, onların miktarı ise sıra ile 46.7 mg g-1 ve 35.9 mg g-1 ’dır. Doğal sepiyolitin maksimum Mn(II) uzaklaştırma miktarı ise 5.2 mg g-1 ’dır. Sepiyolitin NaOH ile modifikasyonu ile arsenik adsorpsiyon kapasitesi dört kata kadar artmış olup, bu değer demir içeren sepiyolit örnekleri ve bimetalik oksitler ile karşılaştırılabilirdir. Langmuir izotermleri SP ile As(V) ve NaSP ile As(III) ayrımı sonuçlarına uyumlu olmasına karşılık Freundlich izoterm modeli SP ile Mn(II) ve Na-SP ile As(V) uzaklaştırmasında uygunluk göstermiştir. Doğal ve modifiye edilmiş sepiyolit ile arsenik ve mangan adsorpsiyonu için kaydırılmış ikinci mertebeden kinetik model iyi uyum sağlamaktadır.Öğe Doğal ve modifiye edilmiş zeolitler yüzeyinde arsenik ve mangan adsorpsiyonun incelenmesi(2014) Ateş, Ayten; Akgül, Gökçen; Belen, Sema Nur; Topçu, Uğur Savaş[Abstract Not Available]Öğe Doğal zeolitlerin yüzeyinde $N_2O$'nun dekompozisyonu ve indirgenmesi(2008) Ateş, Ayten[Abstract Not Available]Öğe Evaluation of characteristics of raw tea waste-derived adsorbents for removal of metals from aqueous medium(Springer Science and Business Media Deutschland GmbH, 2023) Ateş, Ayten; Mert, Yasemin; Timko, Michael T.Chemical modification and microwave activation are cost-effective and eco-friendly engineering methods to improve biochar’s physicochemical and adsorption performance. Therefore, a series of biochars samples was produced by pyrolysis at 500 °C in the presence of phosphoric acid (H3PO4) without and with microwave (MW) irradiation of the raw tea waste (RTW). Effect of acid and MW activation on the characteristics of biochar was compared with biochars produced from pyrolysis of RTW at 300, 500, 700, and 900 °C. Pyrolysis in the presence of H3PO4 promoted the formation of oxygen-containing functional groups and increased the surface area of the biochar product (931 m2 g–1 compared with 13.6 m2 g–1). Compared with biochars obtained from acid-assisted pyrolysis, MW activation nearly doubled the measured surface area (1763 m2 g–1) by the formation of a micropore structure and required seconds instead of hours to perform. Heavy metal adsorption capacities observed for the acid-activated chars were comparable to biochar samples produced in the temperature range of 500–900 °C, but acid-promoted activation required much lower temperatures, and the effects of activation depended on the metal, the solution pH, and the activation treatment. Specifically, acid promotion increased Cu and Cd sorption capacity, attributable to the increased surface area and increased surface densities of oxygen functional groups (C = O and OH). The results of ternary-metal adsorption results demonstrated the competitive adsorption between three metals, and the affinity sequence of biochar produced at 900 °C (BC900) was found as Pb(II) > Cd(II) > Cu(II). However, the metal affinity sequence of BC900 to single metal is Pb(II) > Cu(II) > Cd(II). FTIR and SEM–EDS results revealed that Pb(II) had the same adsorption sites with Cu(II), but Pb(II) has a greater affinity than Cu(II). Kinetic measurements and spectroscopic analysis indicated that Pb, Cu, and Cd form chemical complexes on the surface. These results provide new insight on the utilization of tea wastes for heavy metal removal from aqueous streams. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Öğe Evaluation of Stability and Catalytic Activity in Supercritical Water of Zinc Oxide Samples Prepared by the Sol–Gel Method(Springer, December 2021) Ateş, Ayten; Hatipoğlu, HakanNano-and micro-sized ZnO samples were synthesized by the sol–gel method. Physical and thermal stability of ZnO samples were tested in supercritical water (SCW) and supercritical water gasification (SCWG) of formaldehyde. ZnO calcined at 350 °C (ZnO-350) has spherical particles with an average diameter of 150 nm. After SCW and SCWG treatments, the particle size of ZnO-350 increased and its roughness decreased as a result of agglomeration. Increasing the calcination temperature of ZnO from 350 to 900 °C increased crystallinity and the estimated crystal size of ZnO. The particles of ZnO calcined at 900 °C converted to hexagonal particles from spherical particles by the dissolution of coke precursors in SCW. Compared with the non-catalytic gasification of formaldehyde, the presence of ZnO increased the conversion of formaldehyde and hydrogen formation. The increasing calcination temperatures of ZnO enhanced hydrogen formation, which might be due to the formation of oxygen vacancies on the ZnO1-x.Öğe Oksijen ve diazotmonooksit $(N_2O)$ ile alkanların oksidatif dehidrojenasyonu(2007) Ateş, Ayten; Reitzmann, Andreas[Abstract Not Available]Öğe Süperkritik Su Atmosferinde Gerçekleşen Tepkimelerde Heterojen Katalizörlerin Fiziksel Ve Kimyasal Kararlılığının Belirlenmesi(2017) Ateş, Ayten; Machın, Nesrin Ekinci; Ertaş, Hacı AliBu çalışmada tepkimelerde yaygın olarak kullanılan aktif metal ya da aktif metal taşıyıcı olarak kullanılan ZrO2, CeO2, MoO3, MnxOy (MnO,Mn2O3, MnO2, MnO3), ZnO ve TiO2 katalizörlerinin kimyasal ve yapısal değişimleri, mekanik, kimyasal ve termal kararlılıkları, aktivite ve seçicilikleri formaldehitin ve glikozun süperkritik su gazlaştırılması(SCWG)?nda test edilmiştir. Ticari yöntemle hazırlanmış katalizörlere ek olarak, sol-jel (SJ) ve alev sprey piroliz (FSP) yöntemleri ile sentezlenmiş metal oksitlerin (ZrO2, CeO2, MoO3, MnxOy, ZnO and TiO2) yapılarındaki fizikokimyasal ve kimyasal değişimler SCW atmosferinde ve organik bileşiklerin varlığında deneysel olarak belirlenmiştir. SJ ile hazırlanmış TiO2 örnekleri 350- 900 oC aralığında kalsine edilmiştir. 600 oC?in altında kalsinasyon sıcaklığında anataz fazı ve 800 oC ve 900 oC?de kalsine edilmiş TiO2 örneklerinde ise rutil fazı XRD analizleri ile belirlenmiştir. SCW?de formaldehitin gazlaştırılmasında kullanılmış tüm TiO2 örnekleri aglomerasyona uğramış ve yüzey alanları önemli miktarda azalmıştır. Ayrıca, TiO2 örneklerinin yüzey yükü, oksijen adsorpsiyonu ve indirgenme özelliği önemli ölçüde azalmıştır. Formaldehitin gazlaştırmasında en yüksek hidrojen oluşumu 350 oC?de kalsine edilmiş TiO2 örneğinin varlığında bulunmuştur. SJ ve FSP yöntemi ile MnxOy katalizörleri sentezlenmiş, seçilen yönteme bağlı olarak farklı faz bileşimlerine sahip MnxOy üretilmiştir. SJ ile FSP?den daha büyük parçacık boyutuna sahip MnxOy üretilmiş olup, büyük partikül boyutu SCW?de daha yüksek mekanik stabilite göstermiştir. Benzer bulgular ZrO2?in partikül boyutu için de bulunmuştur. Hem SJ hem de FSP ile sentezlenmiş ZrO2?in monoklinik fazı formaldehitin gazlaştırılmasında hem stabil hem de yüksek hidrojen verimine sahiptir. SJ ve FSP ile sentezlenmiş CeO2 örnekleri kübik CeO2 fazına sahip olup, SCW?de gazlaştırma ile sinterleşmeye ve aglomerasyona uğramıştır. SJ ile sentezlenmiş MoO3, ortorombik yapıya sahiptir. MoO3 formaldehitin gazlaştırılmasında test edildiğinde, MoO3 örneği MoO2?e dönüşmüştür. SCW atmosferinde MoO3 yapısını koruyamamış ve önemli miktarda aglomerasyona uğramıştır. SJ ile hazırlanmış ZnO hekzagonal yapıya sahip olup, 900 oC?de kalsinasyonla sağlanan yüksek parçacık boyutu SCW?a karşı onun stabilitesini artırmıştır. SCW?da glikozun gazlaştırılmasından sağlanan en yüksek hidrojen üretimi SJ ile üretilmiş ZnO ve MnxOy katalizörlerinin varlığında sağlanmıştır.Öğe Synthesis and characterization of molybdenum trioxide with an orthorhombic crystal structure for supercritical water gasification application(Elsevier B.V., 2023) Ateş, Ayten; Hatipoğlu, HakanSupercritical water (SCW) catalytic gasification is promising for the production of synthetic gas from biomass. However, maintaining the activity of heterogeneous catalysts under high pressure and hydrothermal conditions is the most important. Therefore, this study investigates the activity and stability of molybdenum trioxide (MoO3) for the gasification of formaldehyde in SCW. MoO3 with an orthorhombic crystal structure was synthesized by the sol-gel method and tested in the gasification of formaldehyde in SCW. Structural and morphological changes of MoO3 with supercritical water gasification were studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), a scanning electron microscope (SEM), N2 adsorption-desorption, thermogravimetric analysis (TGA), temperature-programmed desorption of oxygen (O2-TPD), temperature-programmed desorption with ammonia (TPD-NH3), and temperature-programmed reaction of hydrogen (H2-TPR). The XRD results show that MoO3 has an orthorhombic crystal structure. Its structure changed to a monoclinic structure upon gasification with supercritical water. SEM images showed that the rod-shaped catalyst particles transformed into thin planar plates at high pressure and temperature conditions in the presence of carbonaceous compounds. H2-TPR and XRD results showed that MoO3 was reduced to MoO2 during SCW gasification with hydrogen and carbonaceous compounds. Moreover, the oxygen stability of the catalyst changed during SCW gasification, and active oxygen species formed on the surface of the catalyst. Compared with homogeneous gasification, in the presence of the MoO3 catalyst, the fractions of CO2 and CH4 increased to 50% and 8.4%, respectively, and the fractions of H2 and CO decreased from 37.8% and 11.8% to 32.2% and 3.9%, respectively, due to the changed decomposition mechanism. Orthorhombic molybdenum oxide can be proposed as a promising catalyst for methane production. © 2022 Elsevier B.V.Öğe The Adsorptive Removal of Arsenic And Manganese from Aqueous Solution by Natural and Modified Sepiolite(Akademik Perspektif Derneği, 2019) Ateş, Ayten; Yaşar, GökhanThe natural sepiolite clay mineral was obtained from General Directorate of Mineral Research and Exploration (MTA) of Turkey and modified with 2.5 M of NaOH. The natural (SP) and modified (Na-SP) sepiolite samples were characterized by XRD, N2 adsorption-desorption, FTIR, SEM-EDS and NH3-TPD. The treatment of the sepiolite with NaOH led to a significant desilication and decationization of the SP. The alkali treatment with NaOH caused solution of silicon and cations, resulting in an increase in its average pore diameter and a decrease in its surface area from 187. 8 m2 g-1 to 7.1 m2 g-1. In addition, a number of weak and medium acid centres of SP was decreased while a number of strong acid centres was increased. The maximum As(III) and As(V) removal with the SP was achieved at an initial pH of 1.5, respectively; ca. 8.9 mg g-1 and 26.8 mg g-1. The maximum removal of As(III) and As(V) with Na-SP was achieved at an initial pH of 5.0; ca. 46.7 mg g-1 and 35.9 mg g-1, respectively. The maximum Mn(II) removal with SP was 5.2 mg g-1. Treatment of SP with NaOH increased its the arsenic adsorption capacity up to four times, which is comparable to iron-containing sepiolite samples and bimetallic oxides. While the Langmuir isotherm fitted well with results obtained from the As(V) with SP and As(III) with Na-SP, the Freundlich isotherm model was more appropriate for the results obtained from As(V) with Na-SP and from Mn(II) of SP. The pseudo-second-order kinetic model for the adsorption of arsenic and manganese on natural and modified sepiolite fitted well.Öğe The effect of microwave and ultrasound activation on the characteristics of biochar produced from tea waste in the presence of H3PO4 and KOH(Springer Science and Business Media Deutschland GmbH, 2023) Ateş, AytenThe mechanism of chemical and physical activation during biomass pyrolysis is crucial for the more effective use of biomass and the preparation of functional porous biochemical materials. In this study, raw tea waste (RTW) was used to prepare the biochar samples by pyrolysis at 300 and 500 °C following phosphoric acid (H3PO4) and potassium hydroxide (KOH) activation along with microwave (MW) and ultrasound irradiation (US). Textural and chemical changes of biochar samples were designed by activation conditions and characterized in detail. SEM and N2 adsorption–desorption results showed that US and MW activation increased dramatically the surface area of the biochar from 942 m2/g to 1984 m2/g in the presence of H3PO4 and from 87 m2/g to 806 m2/g in the presence of KOH. While homogenous cylindrical macropores biochar was produced by acid-assisted US activation, microporous spherical nano-sized particles could be produced by acid-assisted US-MW hybrid activation. Above an optimum US activation time, the pores and channels in the biochar were destroyed and sintering of the particles occurred. Pyrolysis at 300 °C of the RTW activated with KOH led to the hydroxylation and reorganization of oxygen-containing functional groups and C-H groups on the surface. Before pyrolysis, the hybrid activation of biomass by physical and chemical methods can obtain the production of efficient engineered materials with preferable surface area and porosity, composition, and availability of functional groups in many applications, such as catalyst, energy storage and conversion, wastewater treatment, and soil remediation. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
