In the ongoing project, alumina and activated carbon supported catalysts are prepared and tested for H2S decomposition in one-step conventional and/or microwave heating systems. This study was supported by the Scientific and Technological Research Council of Turkey (TUBITAK) under Grant Number 122M400. The authors thank TUBITAK for their support.  Some of the results obtained from the project are published in the article given below.

Related Research Papers about the Decomposition of H2S

[1] Dogan, M. Y., Tasdemir, H. M., Arbag, H., Yasyerli, N., & Yasyerli, S. (2024). H2 production via H2S decomposition over activated carbon supported Fe- and W-catalysts. International Journal of Hydrogen Energy, 75(19), 483-495.

7. Cr- based Catalyst Synthesis for Isobutane Dehydrogenation 

In the research group, studies are carried out on the direct dehydrogenation of isobutane to isobutene, the oxidative dehydrogenation of isobutane, and membrane reactor applications for these reactions. Recently, studies have also begun to obtain isobutene from synthesis gas.

Depending on the development of technology, the demand for valuable products (MTBE, ETBE, BHT, BHA, PIB etc.) has increased, and isobutane dehydrogenation has become an important alternative. Isobutane dehydrogenation is an endothermic equilibrium-limited reaction. High temperatures are required for high conversions. High temperatures, on the other hand, favor coke formation and require frequent regeneration of the catalyst. The reaction at high temperatures causes catalyst deactivation and many side reactions. Catalyst synthesis with high activity, selectivity, and stability is important for this reaction. The reaction proceeds on catalysts with various active components (Pt, V, Cr, Ga, Fe), but the Cr active component attracts attention with its cheapness and suppression of coke formation for the reaction. The different types of Cr that will form on the catalyst are strongly dependent on the preparation method, starting material, and Cr-support interaction. In the study conducted by the research group [1], the effects of Cr content on the catalyst structure, chromate types, and amounts were investigated. The catalyst support MCM-41 was synthesized hydrothermally, and then xCr@MCM-41 (x:4,6,8,10) catalysts in different mass% ratios were prepared by the impregnation technique.  The highest amount of active monochromates for the reaction was detected in the 4Cr@MCM-41 catalyst. Catalytic tests (600°C, atmospheric) were performed on the 4Cr@MCM-41 catalyst, which was selected for its suitable crystal size, homogeneous metal distribution, and high amount of active monochromate. High isobutane conversions (80%) were obtained up to the 60th minute, and high isobutene selectivity (95%) after the 40th minute. The observed high conversions were explained by the conversion of Cr(II)O2-2s formed by tetrahedral coordinated Cr(VI)O4-2 structures in the catalyst into active Cr(III)O3-3 species by using the water in the support structure. In addition, it was shown that this form change reduced the surface acidity of the catalyst, especially the Lewis acid sites, thus increasing the selectivity of isobutene and preventing the formation of coke. It was found that 4% by mass of Cr content from the synthesized xCr@MCM-41 catalysts were suitable for high isobutene selectivity and high amount of monochromate formation. It was aimed to determine the effect of chromium concentration in the catalyst structure on the chromate types and chromium oxidation states in another study conducted by the research group [2]. The MCM-41-supported chromium oxide catalysts at different chromium concentrations (4–10 % by mass) were synthesized hydrothermally. It was shown that inactive α-Cr2O3 crystals for isobutane dehydrogenation increased in the catalyst structure as the chromium loading increased. The highest amount of Cr6+ on the catalyst surface was detected in the catalyst with 4 % chromium by mass. Catalytic tests (T = 600 °C, P = atmospheric pressure, WHSV = 26 h–1) were carried out under fixed bed reactor conditions. The highest isobutane conversion (~60 %) and selectivity (~80 %) were determined on the H4-MCM-41 catalyst, which had the highest amount of Cr6+ and monochromate structures. It was indicated that catalyst deactivation was not due to coke deposition but, rather, was caused by the formation of inactive α-Cr2O3 crystal structures.

The process of oxidative dehydrogenation of light alkanes can utilize heterogeneous catalysis in the presence of carbon dioxide (CO2). This approach is sustainable and environmentally friendly as CO2 is a softer and controllable option for converting light alkanes into olefins. By introducing an oxidizing agent to the dehydrogenation reaction environment, the hydrogen produced during the process can be oxidized, which helps to reduce the occurrence of side reactions such as alkane cracking and coke formation. In the research group study [3], chromium-based catalysts on titanium-modified MCM-41 were synthesized for oxidative dehydrogenation reactions. To increase the hydrothermal stability of support, titanium was added to the MCM41. The hydrothermal stability test indicated that the loading of titanium improved the stability of MCM-41. Chromium-based catalysts on titanium-modified MCM-41 were prepared by wet impregnation method at different chromium loading (3% and 10%, by mass). The highest isobutane conversion (94%) and isobutene selectivity (81%) values were obtained for catalyst supported on Ti-modified MCM-41. High activity predicted for catalyst supported on modified MCM-41 was explained by improving hydrophilic properties.

Related Research Papers about Cr- based Catalyst Synthesis for Isobutane Dehydrogenation:

[1] Çetinyokuş Kılıçarslan, S., Doğan, M., Erol, Z. (2021). Investigation of the effectiveness of Cr@MCM-41 catalysts in isobutane dehydrogenation, Journal of the Faculty of Engineering and Architecture of Gazi University, 36(2), 1075-1088.

[2] Erol, Z., Çetinyokuş Kılıçarslan, S., Doğan, M. (2020). Investigation of isobutane dehydrogenation on CrOx/MCM-41 Catalyst. Macedonian Journal of Chemistry and Chemical Engineering, 39(1), 109–118.

[3] Mosa, H.M.Y., Dogan, M., Cetinyokus, S. (2024). Synthesis and characterization of chromium-b Catalysts on titanium-modified-MCM-41 for oxidative dehydrogenation of isobutane. Bitlis Eren University Journal of Science and Technology, 14(1), 1-22.

8. Investigation of Isobutane Dehydrogenation in Pd-based Membrane Reactors

Pd and Pd alloy membranes, which are highly selective towards hydrogen, are widely used in dehydrogenation and hydrogenation reactions. Pd membranes must have a certain thickness to maintain their mechanical strength and when made thin enough they can provide adequate flow for hydrogen. It is recommended to use palladium in alloys with other metals to increase hydrogen permeability. It was aimed to synthesize PdCu alloy membranes with firm, thin, and fcc phase structures (resistant to sulfur compounds), selectively permeable to hydrogen, using an electroless plating technique by creating an osmotic flux by the research group [1]. First, coating studies were conducted without creating osmotic flux to determine the appropriate alloy formation temperature. Commercial porous borosilicate glass tubes were modified with alumina to form an interface that enhances the interaction between the coating and the support. Afterward, coating studies were conducted by creating an osmotic flux with a 3 M sucrose solution, keeping the coating conditions and bath composition the same. By the literature, low hydrogen flux (0.04–0.09 mol/m2 s) and high selectivity values (αH2/N2:465–324) were determined in membranes synthesized with osmotic flux. Additionally, it was determined that this membrane remained stable in the hydrogen environment (T = 250 °C, ΔP = 203 kPa) for 96 h. The results of the study showed that conducting the electroless plating method with osmotic flux made positive contributions to the structure and hydrogen selectivity of the prepared alloy membranes. 

Membrane reactors are reactors that perform catalytic reactions and separation processes in one step. This combination reduces the number of reactors, and the amount of catalyst and makes the process more efficient. The use of membrane reactors in equilibrium-limited dehydrogenation reactions is remarkable. One of the studies [2], it was aimed to overcome the equilibrium conversions by using a membrane reactor. First, Al2O3-supported chromium-based catalysts were prepared by the impregnation technique. Then, reactions were performed with a catalyst containing 8% by mass of Cr, which was prepared in a mixing time of 48 h with the highest amount of monochromate. The reactions were carried out in a Pd-based membrane reactor system with pure isobutane feed. The effect of reactor temperature was investigated at 550 °C and 600 °C (WHSV:0.3h−1). While no significant difference was observed between the conversion values at both reactor temperatures (⁓90%), isobutene selectivity values were higher (⁓85%) at 600 °C. The presence of less hydrogen in the environment decreased the formation of the hydrogenation reaction of isobutane. This situation enhanced an increase in isobutene selectivity values. The results of the modeling studies carried out in the membrane reactor were found to be compatible with the experimental results. 

Related Research Papers about Isobutane Dehydrogenation in Pd-based Membrane Reactors:

[1] Kilic, S., Dogan, M., Cetinyokus, S. (2023). Effects of osmotic flux on PdCu alloy membrane structure.  Arabian Journal for Science and Engineering, 48, 8887–8899.

[2] Erdali, A.D., Cetinyokus, S., Dogan, M. (2022). Investigation of isobutane dehydrogenation on CrOx/Al2O3 catalyst in a membrane reactor. Chemical Engineering and Processing - Process Intensification, 175, 108904.

9. Computational and Electrochemical Studies

Data mining strategies have emerged as a transformative trend in recent years across various scientific fields, ranging from astronomy and biology to economics. These techniques hold significant promise for advancing fuel cell technologies as well. In the research, we apply data mining strategies and machine learning techniques to the field of electrocatalysis, leveraging these powerful tools to unlock new insights. The studies span a wide range of applications, from biodiesel production and food science to cutting-edge fuel cell research and even to SARS-CoV-2 glucometer. Such data-driven approaches not only provide robust frameworks for analyzing complex experimental data but also help researchers identify promising directions for future fuel cell technologies. With the ever-expanding scientific literature, these strategies are invaluable for navigating and building upon the growing body of knowledge. The research focuses on the collection, filtering, and visual analysis of experimental observations, alongside the application of both supervised and unsupervised machine learning methods. These include techniques like regression, classification trees, artificial neural networks, Gaussian process regression, association rule mining, and SHAP (SHapley Additive exPlanations), among others. We employ a variety of software tools such as AutoQSAR, Shapash, Python libraries, MATLAB tools, and custom code to enhance the scope and accuracy of the analyses. Below are some of the recent publications, showcasing the ongoing efforts in applying machine learning to fuel cell technology and other areas:

Related Research Papers about Computational and Electrochemical Studies:

[1] Günay, M. E., & Tapan, N. A. (2024). Analysis of CO selectivity during electroreduction of CO2 in deep eutectic solvents by machine learning. Journal of Applied Electrochemistry, 54(7), 1541-1556.

[2] Gürbüz, T., Günay, M. E., & Tapan, N. A. (2024). Machine learning solutions for enhanced performance in plant-based microbial fuel cells. International Journal of Hydrogen Energy, 78, 1060-1069.

[3] Günay, M. E., & Tapan, N. A. (2023). Evaluation of polymer electrolyte membrane electrolysis by explainable machine learning, optimum classification model, and active learning. Journal of Applied Electrochemistry, 53(3), 415-433.

[4] Günay, M. E., & Tapan, N. A. (2023). Analysis of PEM and AEM electrolysis by neural network pattern recognition, association rule mining, and LIME. Energy and AI, 13, 100254.

[5] Tapan, N. A., Günay, M. E., & Yıldırım, N. (2023). Application of Machine Learning for the Determination of Damaged Starch Ratio as an Alternative to Medcalf and Gilles Principle. Food Analytical Methods, 16(3), 604-614.

[6] Tapan, N. A. (2022). Application of Gaussian process regression and asymmetric least squares baseline algorithm on the determination of electrochemical sensor characteristics: A case study on SARS-CoV-2 glucometer. Chemometrics and Intelligent Laboratory Systems, 230, 104677.

[7] Günay, M. E., Türker, L., & Tapan, N. A. (2019). Significant parameters and technological advancements in biodiesel production systems. Fuel, 250, 27-41.

10. Microwave Reactor Technology for Catalytic Reaction Studies

In the laboratory, a microwave reactor system has been used for catalytic decomposition of non-carbonaceous, such as ammonia, as well as carbonaceous feed, such as methane, to produce hydrogen with high purity. For this aim, we are also working to synthesize novel heterogeneous catalysts. Microwave reactor system provides different advantages, such as lower reaction temperature for higher conversion and selectivity, easy control, and energy efficiency, as compared to conventionally heated reactor systems, especially for endothermic reactions.  A photograph of the experimental setup is shown in Figure 5. The microwave reactor (MW) operated continuously, using a microwave generator (supplied by SAIREM) with up to 2 kW power at 2.45 GHz, a magnetron, a chiller to cool the system, and a microwave heating chamber where the quartz reactor was placed. The reaction temperature was easily adjusted by modifying the power input to the generator. One key advantage of the microwave system was its ability to increase the reactor temperature from room temperature to 300°C in under a minute. We also compare the results obtained with a microwave reactor system with the ones obtained using a conventional system.  The conventional system used for comparison is an electrically heated tubular furnace. In both setups, a gas chromatograph with a thermal conductivity detector (TCD) enabled online analysis of reactants and products.