Optimization of the partial oxidation of methane on ni mgo α alumina monolith catalyst in a reverse flow reactor using the method of steepest ascent

De La Salle University OPTIMIZATION OF THE PARTIAL OXIDATION OF METHANE ON Ni-MgO/α-ALUMINA MONOLITH CATALYST IN A REVERSE FLOW REACTOR USING THE METHOD OF STEEPEST ASCENT A Thesis presented to the Faculty of the Graduate School of Chemical Engineering College of Engineering DE LA SALLE UNIVERSITY – MANILA In Partial Fulfillment of the Requirements for the Degree of Master of Science in Chemical Engineering By Trung Kim Nguyen Thesis Adviser Prof Dr Luis F Razon Thesis Co-Adviser Prof Dr Raymond R Tan Prof Dr Hirofumi Hinode November, 2009 De La Salle University De La Salle University ACKNOWLEDGEMENT This thesis is dedicated to Almighty God who is the source of wisdom and knowledge and thank God for giving me the strength, guidance and patience to overcome so many problems to accomplish my thesis ¾ I would like to thank The ASEAN University Network Southeast Asia Engineering Education Development Network (AUN/SEED-Net) for its financial support and for giving me an opportunity to study in De La Salle University - Manila ¾ I am indebted to De La Salle University for furnishing very good facilities and the best conditions to finish the experiments I am very pleased to be a student of De La Salle University ¾ I want to express my deepest gratitude to Dr Luis Razon, my thesis adviser, for inspiring and helping me to overcome many difficulties during my experiments This thesis would not have been possible without your support Thank you for patiently editing my thesis and giving me a lot of valuable comments and suggestions during my experiments and thesis-writing Your instructions and tolerance have always been appreciated ¾ I owe my deep gratitude to my thesis co-adviser, Dr Raymond Tan, whose guidance and support enabled me to develop a deeper understanding of this topic Thank you for spending time to correct my thesis ¾ I also want to thank my Japanese coadviser, Dr Hirofumi Hinode, for giving us instructions and support when they are needed and spending valuable time to visit and help us in De La Salle University ¾ I am heartily thankful to my thesis panel, Dr Joseph Auresenia (panel chair), Dr Leonila Abella, Dr Susan Gallardo for offering me a lot of comments and suggestions to improve my thesis ¾ To Ms Gladys Cruz, thank you for taking care of me in Manila Your encouragements and prayers for me are also very much appreciated De La Salle University ¾ To Mr Dennis Yu, thank you for purchasing all equipment and tools which are necessary for my experiments ¾ To the technicians of the Chemical Engineering Department, Mr Benjamin Cardoza, Mr Peter Ascrate, Mr Manny Burgos, Mr Judito Valdez, Mr Ismael Serrano, thank you so much for your assistance during my experiments This thesis could not have beeen accomplished without you ¾ To the technicians of the Mechanical Engineering Department, Mr Ricky Aldanesa and Mr Fernando Barroz, thank you for cutting the monolith and your consideration regarding my thesis ¾ To Mr Phan Huy, thank you for guiding me how to use the set-up and the GC ¾ To Mr Anton Purmono and Mr Teddy Monroy, thank you for your instructions to troubleshoot my GC problems ¾ To Mr Tran Hai Ung, thank you for manufacturing this reverse flow reactor and guiding me how to repair it ¾ To Mr Adore Nonato, thank you for kindly helping me to repair the reactor and for your patience when the reactor had to be fixed many times ¾ I also want to thank all my friends, especially Mr Nguyen Tuan Anh, Ms Nguyen Thi Anh Nga and Ms Nguyen Ngoc Diem Phuong for sharing the life experiences and for your assistance in numerous ways during my study Thank you for making my life unforgettable ¾ I also would express my gratitude to my parents, my brothers, my sister-in-law and my girlfriend who have always taken interest in my study and my life in Manila Thank you so much for your prayers and your encouragements Finally, I want to offer my regards and blessings to all of those who supported me in any respect during my study in De La Salle University God bless you all! De La Salle University ABSTRACT Catalytic partial oxidation of methane (CPOM) has been recognized as a suitable method to produce synthesis gas for production of liquid fuel and hydrogen CPOM, which is a mildly exothermic reaction, can be conducted autothermally in a reverse flow reactor (RFR) wherein the direction of flow is reversed cyclically Implementation of real RFR is complicated Recent published studies have focused mainly on numerical simulation and control strategy, but there have been few published experimental studies This study describes a systematic experimental optimization of a laboratory scale RFR for CPOM on Ni-MgO/α-Al2O3 monolith catalyst using the response surface methodology The effect of initial temperature (Tini), switching time (τ), total flowrate (F), molar feed ratio between methane and oxygen (M), and catalyst length were investigated Hydrogen yield and methane conversion are used as the experimental responses The steepest ascent path was established based on the first experimental design to determine the stationary point whose nature was confirmed by the second experimental design The iteration of establishing the steepest ascent path and experimental design was done until the maximum point was specified In this study, the optimum operating conditions were determined in the second experimental design The analysis of reactor operation proved to be challenging due to the complex interplay of the different experimental factors The following interactions were found to be significant for methane conversion: M*τ, F*τ and M*F The interaction of F*τ also affected the hydrogen yield The third order interaction of F*τ*M was also found to be statistically significant The optimum methane conversion value of 56.38% could be obtained by setting switching time, total flowrate and molar ratio of 4.24 minutes, 543ml/min and 1.575, respectively The optimum value of hydrogen yield of 35.91% was reached by setting total flowrate, molar feed ratio and switching time of 540ml/min, 1.442 and 4.15 minutes, respectively De La Salle University TABLE OF CONTENTS TABLE OF CONTENTS i  LIST OF FIGURES vi  LIST OF TABLES viii  NOMENCLATURE ix  Chapter INTRODUCTION 1  1.1  Background of the study 1  1.2  Statement of the problem 3  1.3  Objectives of the study 4  1.4  Significance of the study 5  1.5  Scope and limitations 6  Chapter REVIEW OF RELATED LITERATURE 9  2.1  Modification of reverse flow operation 9  2.2  Review of recent studies in reverse flow reactor 10  2.2.1  Control of reverse flow reactor 11  2.2.2  Partial oxidation of methane in reverse flow reactor 12  2.3  Optimization of cyclic processes 14  2.4  Optimization of catalytic reactors 16  2.4.1  Genetic algorithms in optimization catalytic reactor 17  2.4.2  Response surface methods in optimization of catalytic reactors 19  2.5  Optimization of reverse flow reactors 21  2.6  The method of steepest ascent in optimization 23  2.7  Related studies in De La Salle University - Manila 24  Chapter THEORETICAL CONSIDERATIONS 26  3.1  Partial Oxidation of Methane (POM) 26  3.1.1  3.1.1.1  Thermodynamics of POM 27  Effects of temperature 28  i De La Salle University 3.1.1.2  Effects of molar feed ratio 29  3.1.1.3  Effects of pressure 29  3.1.2  Mechanism of Gas-Phase POM 30  3.1.2.1  The Direct Mechanism 30  3.1.2.2  The Pyrolysis Mechanism 31  3.1.2.3  Two-step mechanism through complete oxidation 31  3.1.2.4  Mechanism on the catalyst 32  3.1.3  Catalysts for the POM 34  3.1.3.1  Active Components 34  3.1.3.2  Catalyst Supports 35  3.1.3.3  Catalyst Promoters 35  3.1.4  Monolith structure of the catalyst 36  3.1.5  Characterization of Ni-MgO/αAl2O3 monolith catalyst 37  3.1.6  Flammability Limits of Methane 37  3.2  Factors affecting reverse flow reactor performance 38  3.2.1  Initial conditions 39  3.2.1.1  Initial Temperature Profile 39  3.2.1.2  Initial Flowrate 40  3.2.2  Operating Parameters 41  3.2.2.1  Molar Feed Ratio 41  3.2.2.2  Switching Time 41  3.2.2.3  Flowrate of Feed Gas 42  3.2.3  Design parameters 42  3.2.4  Interaction between independent variables 43  3.3  3.2.4.1  Switching Time and Feed Flowrate 43  3.2.4.2  Switching Time and Catalytic Length 43  Performances of reverse flow reactor 44  3.3.1  Temperature profile at cyclic steady state 44  3.3.2  The concentration of effluent gas 45  ii De La Salle University 3.4  Determination of cyclic steady state 46  3.4.1  Definition based on the repeatability of the process behavior 46  3.4.2  Thermodynamic definition 46  3.4.3  Approach to cyclic steady state of reverse flow reator 47  3.5  Theory of experimental optimization 50  3.5.1  The steepest ascent method 50  3.5.2  Ridge Analysis 51  3.5.3  Canonical Analysis 54  3.5.4  Multiple responses 55  3.5.4.1  The weighted priorities strategy 55  3.5.4.2  The desirability approach 56  3.5.4.3  The mathematical programming approach 58  Chapter METHODOLOGY 60  4.1  Preparation of NiO-MgO/α-Al2O3 catalyst 61  4.2  Coating NiO-MgO/α-Al2O3 catalyst on monoliths 62  4.2.1  Preparation of coating slurry 62  4.2.2  The coating procedure 63  4.3  Experimental set-up 64  4.3.1  Description of the set-up 64  4.3.2  Operation of the set-up 66  4.3.2.1  Preparation before start-up 66  4.3.2.2  Start-up procedure 67  4.3.2.3  Reverse flow operation of the reactor 68  4.3.2.4  Extinction of the reverse flow reactor 69  4.3.2.5  The reverse flow reactor in cyclic steady state 70  4.4  Activity Test 71  4.5  Strategy of data analysis 71  4.6  SAS/STAT® Software 72  iii De La Salle University 4.7  Factor space boundaries 72  Chapter RESULTS AND DISCUSSION 75  5.1  Initial experimental design 75  5.1.1  Interaction between initial temperature and catalyst length 77  5.1.2  Interaction between molar feed ratio and total flowrate 78  5.1.3  Interaction between molar feed ratio and switching time 80  5.1.4  Interaction between total flowrate and switching time 81  5.1.5  Summary from the initial experimental design 82  5.2  Effect of initial temperature 83  5.3  The steepest ascent path 84  5.4  The second experimental design 85  5.4.1  Regression results 87  5.4.1.1  Regression results of methane conversion 87  5.4.1.2  Regression results of hydrogen yield 88  5.4.2  Meaning of quadratic and linear effects 90  5.4.2.1  Quadratic and linear effects on methane conversion 90  5.4.2.2  Quadratic and linear effects on hydrogen yield 92  5.4.3  Meaning of interaction effects 93  5.4.4  Meaning of third-order interactions 94  5.4.5  Optimum Points 96  5.5  Activity of catalyst 98  5.5.1  Results of activity test 98  5.5.2  Effects of in-use time 99  5.5.3  Effects of the number of times the catalyst was reduced 100  Chapter CONCLUSIONS AND RECOMMENDATIONS 102  6.1  Conclusions 102  6.2  Recommendations 103  Reference 105  iv De La Salle University Appendix Specifications of Materials 115  Appendix Activity Test 116  Appendix The face-centered experimental design 117  Appendix The Canonical Analysis 118  Appendix The comparisons of the experiments to the theoretical equilibrium data 119  Appendix The experimental data 120  v De La Salle University Salomons, S., Hayes, R.E., Poirier, M., Sapoundjiev, H., (2003) “Flow reversal reactor for the catalytic combustion of lean methane mixtures”, Catalyst Today 83, p59 Silva, C.M., Biscaia, E.C., (2003) “Genetic algorithm development for multiobjective optimization of batch free-radical polymerization reactors”, Computers and Chemical Engineering 27, p1329-1344 Smet, C.E.H, (2000) “Partial Oxidation of Methane to synthesis Gas: Reaction Kinetics and Reactor Modelling”, Eindhoven University of Technology, Terneuzen, The Netherlands ISBN 90-386-2921-4 Smet, C.R.H., Berger, M.H.J.M., Marin, R.J., Schouten, G.B., (2001) “Design of adiabatic fixed-bed reactors for the partial oxidation of methane to synthesis gas Application to production of methanol and hydrogen-for-fuel-cells”, Chemical Engineering Science.56, p4849–4861 Smit, J., Bekink, G.J., Annaland, M.V.S., Kuipers, J.A.M., (2007) “Experimental demonstration of the reverse flow catalytic membrane reactor concept for energy efficient syngas production Part 1: Influence of operating conditions”, Chemical Engineering Science 62, p1239 – 1250 Steghuis, A G., Ommen, J G., Seshan, K., Lercher, J.A., (1997) “New Highly Active Catalysts in Direct Partial Oxidation Methane to Synthesis Gas”, In Proceedings 4th International Natural Gas Conversion Symposium Conference 107, p403-408 Tran, H.U., Razon L.F., Garlarso, S.M., Aida, T., (2007) “Experiment on a reverse flow reactor for producing synthesis gas using methane partial oxidation over NiO-MgO/α-Al2O3”, Regional Symposium on Chemical Engineering (RSCE) 2007 Indonesia The experimental results were revised on May 2008 by the authors 112 De La Salle University Trimm, D L., Lam, C W., (1980a) “The combustion of methane on platinum— alumina fibre catalysts—I : Kinetics and mechanism”, Chemical Engineering Science 35(6), p1405-1413 Trimm, D L., Lam, C W., (1980b) “The combustion of methane on platinum— alumina fibre catalysts—II design and testing of a convective-diffusive type catalytic combustor”, Chemical Engineering Science, 35(8), p1731-1739 Unger, J., Kolios, G., Eigenberger G., (1997) “On the efficient simulation and analysis of regenerative processes in cyclic operation”, Computers & Chemical Engineering 21, pS167-S172 van Noorden, T.L., Lunelc, S.M.V., Blieka A., (2003) “Optimization of cyclically operated reactors and separators”, Chemical Engineering Science 58, p4115 – 4127 Vergunst, T., Linders, M.J.G., Kapteijn, F., Moulijn, J.A., (2001) “Carbon based monolithic structures”, Catalysis Review 43(3), p291–314, Marcel Dekker, Inc Veser, G., Frauhammer, J., Friedle U., (2000) “Syngas formation by direct oxidation of methane: Reaction mechanisms and new reactor concepts”, Catalysis Today 61(1-4), p55-64 Wang, J., Wan, W., (2008) “Experimental design methods for fermentative hydrogen production: A review”, International Journal of Hydrogen Energy 34,1 p 235-244 Wang, K., Qian, Y., Yuan Y., Yao, P., (1998) “Synthesis and optimization of heat integrated distillation systems using an improved genetic algorithm”, Computers and Chemical Engineering 23(1), p125–136 Wong, C., Bonvin,D., Mellichamp A.D., Rinker, R.G., (1983) “On controlling an autothermal fixed-bed reactor at an unstable state- IV Model fitting and control of the laboratory reactor”, Chemical Engineering Science 38, p619633 113 De La Salle University Xu, J., Froment, G F (1989a) “Methane steam reforming, methanation and watergas shift: Intrinsic kinetics, A.I.Ch.E Journal 35, p88-96 Xu, J., Froment, G F (1989b) “Methane steam reforming: II Diffusional limitations and reactor simulation”, A.I.Ch.E Journal 35, p97-103 Yee, A.K.Y., Ray, A K., Rangaiah, G.P., (2003) “Multiobjective optimization of an industrial styrene reactor”, Computers and Chemical Engineering 27, p111-130 Zhou, X.G, Yuan W.K., (2005) “Optimization of the fixed-bed reactor for ethylene epoxidation”, Chemical Engineering and Processing 44, p1098–1107 Zhu, J., (2001) “A feasibility study of CH4 reforming by partial oxidation”, PhD Thesis, Curtin University of Technology Zhu, J., Rahuman, M.S.M.M., Ommen, J.G, V., Lefferts, L., (2003) “Dual catalyst bed concept for catalytic partial oxidation of methane to synthesis gas”, Applied Catalysis A: General 259 p95-100 Zwinkels, M.F.M, Jaras, S.G., Menon, P.G., (1995) “Preparation of catalyst VI”, Elsevier, Amsterdam, p.85 114 De La Salle University Appendix Specifications of Materials Chemicals Nickel Nitrate Ni(NO3)2.6H2O Magnesium Nitrate, Mg(NO3)2.6H2O Ammonium Hydroxide NH4OH Nitric acid, HNO3 Aluminum Oxide, α-Al2O3 Aluminum Oxide, γ-Al2O3 Methane, CH4 Oxygen, O2 Nitrogen, N2 Helium, He Hydrogen, H2 Carbon Monoxide, CO Carbon Dioxide, CO2 Cordierite monolith Specifications Purity 98%, Analytical Grade from Sigma Aldrich, Purity 99%, Analytical Grade from Sigma Aldrich Reagent Grade, 28-30% from J.T.Baker Reagent Grade, 69-70% from J.T.Baker Purity 99.7%, from J.T.Baker, powder form Purity 99.99%, Analytical Grade, from Advanced Materials® , powder form CIGI; ultra high purity compressed gas CIGI; high purity 99.99 % compressed gas CIGI; high purity 99.99 % compressed gas CIGI; high purity 99.99 % compressed gas CIGI; high purity 99.99 % compressed gas CIGI; high purity 99.99 % compressed gas CIGI; high purity 99.99 % compressed gas 400 cpsi (cell per square inch) 115 De La Salle University Appendix Activity Test Temperature (oC) Methane Conversion Hydrogen Yield Used New Used New catalyst Catalyst Catalyst catalyst 400 1.10% 1.22% 0.45% 0.65% 500 24.95% 29.50% 4.98% 5.26% 550 30.17% 32.10% 6.53% 7.82% 600 34.15% 36.51% 15.23% 17.60% 650 51.23% 52.60% 48.96% 50.10% 700 69.25% 70.10% 65.97% 67.81% 750 79.81% 81.20% 77.64% 78.20% 800 96.30% 94.32% 92.17% 94.30% 116 De La Salle University Appendix The face-centered experimental design The second experimental design Factors Initial Temperature(oC) Catalyst length (mm) Total flowrate (ml/min) Switching time (minutes) Molar feed ratio Low limit 888 270 480 3.42 1.2 Center point 888 270 550 4.21 1.55 High limit 888 270 620 5.00 1.9 Fixed value Fixed value Face-centered CCD Face-centered CCD Face-centered CCD The Central Composite Face-centered Design Run No 10 11 12 13 14 15 16 17 18 19 20 Tini (oC) 888 888 888 888 888 888 888 888 888 888 888 888 888 888 888 888 888 888 888 888 L (mm) 270 270 270 270 270 270 270 270 270 270 270 270 270 270 270 270 270 270 270 270 F (ml/min) 480 620 480 620 480 620 480 620 480 620 550 550 550 550 550 550 550 550 550 550 τ (min) 3.42 3.42 5.00 5.00 3.42 3.42 5.00 5.00 4.21 4.21 3.42 5.00 4.21 4.21 4.21 4.21 4.21 4.21 4.21 4.21 117 M Note 1.20 1.20 1.20 1.20 1.90 1.90 1.90 1.90 1.55 1.55 1.55 1.55 1.20 1.90 1.55 1.55 1.55 1.55 1.55 1.55 Factorial Design Factorial Design Factorial Design Factorial Design Factorial Design Factorial Design Factorial Design Factorial Design Star point Star point Star point Star point Star point Star point Center point Center point Center point Center point Center point Center point De La Salle University Appendix The Canonical Analysis The canonical analysis of methane conversion on the second design Eigenvalue Eigenvector Total flowrate Switching Time Molar feed ratio -4.870550 -0.648404 0.172525 0.741490 -5.469883 0.466752 -0.679361 0.566225 -6.428204 0.601427 0.713235 0.359974 Stationary point 543.07 ml/min 4.24 1.57 Stationary point is maximum The predicted methane conversion at this stationary point: 57.27% The predicted hydrogen yield at this stationary point: 35.48% The canonical analysis of hydrogen yield on the second design Eigen value Eigen vector Total flowrate Switching Time Molar feed ratio -1.951277 0.272869 0.313235 0.909630 -4.228321 0.953631 -0.212891 -0.212759 -8.361766 0.127008 0.925506 -0.356802 Stationary point 540.37 ml/min 4.15 1.44 Stationary point is maximum The predicted hydrogen yield at this stationary point: 35.91% The predicted methane conversion at this stationary point:56.38% 118 De La Salle University Appendix The comparisons of the experiments to the theoretical equilibrium data Run No 10 11 12 13 14 15 16 17 18 19 20 Final Methane Conversion Temperature Experimental Theoretical (oC) 540 34.50 76.0 650 46.45 95.4 750 48.06 98.6 650 36.40 95.4 750 48.90 97.2 400 37.10 45.8 500 41.32 54.3 580 45.48 71.0 600 53.20 80.6 600 50.66 80.6 620 51.50 85.4 700 51.61 96.4 750 52.52 98.6 700 51.94 95.3 750 62.43 97.9 750 61.11 97.9 720 57.87 97.9 720 58.90 97.9 750 60.46 97.9 750 56.60 97.9 Hydrogen Yield Experimental Theoretical 28.50 28.29 21.40 15.10 15.90 17.95 21.15 24.63 32.64 26.48 21.89 30.39 30.28 31.35 38.89 37.71 37.21 36.27 36.37 35.43 69.0 82.8 85.0 82.8 71.0 38.7 55.8 67.3 74.4 74.4 76.8 76.6 85.0 69.9 78.0 78.0 77.1 77.1 78.0 78.0 This table represents the comparison between experimental results and theoretical thermodynamic equilibrium data which is calculated by Enger, Lodeng and Holmen (2008) The conditions that each run was conducted should be referred to the second table of Appendix The Run No is still consistent for the reference 119 De La Salle University Appendix The experimental data Experiments of the second experimental design Run No 1: Tini=888oC, L= 270mm, F=480ml/min, τ=3.42min, M=1.2 Run No 2: Tini=888oC, L= 270mm, F=620ml/min, τ=3.42min, M=1.2 Run No 3: Tini=888oC, L= 270mm, F=480ml/min, τ=5min, M=1.2 Run No 4: Tini=888oC, L= 270mm, F=620ml/min, τ=5min, M=1.2 120 De La Salle University Run No 5: Tini=888oC, L= 270mm, F=480ml/min, τ=3.42min, M=1.9 Run No 6: Tini=888oC, L= 270mm, F=620ml/min, τ=3.42min, M=1.9 Run No 7: Tini=888oC, L= 270mm, F=480ml/min, τ=5min, M=1.9 Run No 8: Tini=888oC, L= 270mm, F=620ml/min, τ=5min, M=1.9 121 De La Salle University Run No 9: Tini=888oC, L= 270mm, F=480ml/min, τ=4.21min, M=1.55 Run No 10: Tini=888oC, L= 270mm, F=620ml/min, τ=4.21min, M=1.55 Run No 11: Tini=888oC, L= 270mm, F=550ml/min, τ=3.42min, M=1.55 Run No 12: Tini=888oC, L= 270mm, F=550ml/min, τ=5min, M=1.55 122 De La Salle University Run No 13: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.2 Run No 14: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.9 Run No 15: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 Run No 16: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 123 De La Salle University Run No 17: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 Run No 18: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 Run No 19: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 Run No 20: Tini=888oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 124 De La Salle University The experimental data with the different initial temperatures Run No 1: Tini=750oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 Run No 2: Tini=819oC, L= 270mm, F=550ml/min, τ=4.21min, M=1.55 The experimental data on the steepest ascent path Run No 3: Tini=878oC, L= 240mm, F=497.5ml/min, τ=3.36min, M=1.68 Run No 2: Tini=863oC, L= 180mm, F=550ml/min, τ=4.21min, M=1.68 125 De La Salle University Run No 1: Tini=853oC, L= 120mm, F=492ml/min, τ=2.96min, M=1.94 126 ... synthesis gas by the partial oxidation of methane The catalyst in the partial oxidation of methane has an important role Mitri et al (2004) investigated the catalytic partial oxidation of methane. .. yield and methane conversion from partial oxidation of methane on NiO -MgO/ α- alumina monolith catalyst in a reverse flow reactor be attained through the use of the method of steepest ascent? 1.3... shorten the contact time The study may offer a comprehensive solution for partial oxidation of methane Studies of partial oxidation of methane on structured catalyst, like monolith catalyst in a reverse