Lanthanum oxide promoted cobalt catalyst supported on mesoporous alumina for syngas production via methane dry reforming

LANTHANUM OXIDE-PROMOTED COBALT CATALYST SUPPORTED ON MESOPOROUS ALUMINA FOR SYNGAS PRODUCTION VIA METHANE DRY REFORMING TRAN NGOC THANG DOCTOR OF PHILOSOPHY UNIVERSITI MALAYSIA PAHANG UNIVERSITI MALAYSIA PAHANG DECLARATION OF THESIS AND COPYRIGHT Author’s Full Name : TRAN NGOC THANG Date of Birth : 20th NOVEMBER 1982 Title : LANTHANUM OXIDE-PROMOTED COBALT CATALYST SUPPORTED ON MESOPOROUS ALUMINA FOR SYNGAS PRODUCTION VIA METHANE DRY REFORMING Academic Session : SEMESTER 2021/2022 I declare that this thesis is classified as:  CONFIDENTIAL  RESTRICTED  OPEN ACCESS (Contains confidential information under the Official Secret Act 1997)* (Contains restricted information as specified by the organization where research was done)* I agree that my thesis to be published as online open access (Full Text) I acknowledge that Universiti Malaysia Pahang reserves the following rights: The Thesis is the Property of Universiti Malaysia Pahang The Library of Universiti Malaysia Pahang has the right to make copies of the thesis for the purpose of research only The Library has the right to make copies of the thesis for academic exchange Certified by: _ (Student’s Signature) C3811844 New IC/Passport Number Date: 04 January 2022 _ (Supervisor’s Signature) Ts Dr Sumaiya bt Zainal Abidin @ Murad Name of Supervisor Date: 04 January 2022 NOTE: * If the thesis is CONFIDENTIAL or RESTRICTED, please attach a thesis declaration letter SUPERVISOR’S DECLARATION We hereby declare that we have checked this thesis and in our opinion, this thesis is adequate in terms of scope and quality for the award of the degree of Doctor of Philosophy _ (Supervisor’s Signature) Full Name : TS DR SUMAIYA BT ZAINAL ABIDIN @ MURAD Position : ASSOCIATE PROFESSOR Date : 04 JANUARY 2022 _ (Co-supervisor’s Signature) Full Name : DR NURUL AINI BINTI MOHAMED RAZALI Position : ASSOCIATE PROFESSOR Date : 04 JANUARY 2022 STUDENT’S DECLARATION I hereby declare that the work in this thesis is based on my original work except for quotations and citations which have been duly acknowledged I also declare that it has not been previously or concurrently submitted for any other degree at Universiti Malaysia Pahang or any other institutions _ (Student’s Signature) Full Name : TRAN NGOC THANG ID Number : PKC18003 Date : 04 JANUARY 2022 LANTHANUM OXIDE-PROMOTED COBALT CATALYST SUPPORTED ON MESOPOROUS ALUMINA FOR SYNGAS PRODUCTION VIA METHANE DRY REFORMING TRAN NGOC THANG Thesis submitted in fulfillment of the requirements for the award of the degree of Doctor of Philosophy College of Engineering UNIVERSITI MALAYSIA PAHANG JANUARY 2022 ACKNOWLEDGEMENTS I would like to express my honest gratefulness to my supervisor, Assoc Prof Dr Sumaiya bt Zainal Abidin @ Murad for her meaningful guidance and support throughout the difficult time in the COVID-19 pandemic condition She always encouraged me with her outstanding experience and valuable awareness I also would like to thank my exmain supervisor Dr Vo Nguyen Dai Viet for his constant support He has imparted me with professional knowledge and unique insights as well as useful research skills in the reaction engineering and heterogeneous catalysis field for nurturing me as a qualified academician I also wish to acknowledge my co-supervisor, Assoc Prof Dr Nurul Aini Mohamed Razali for her suggestions and cooperation throughout the study I appreciate the co-operation and information sharing in this research from all my colleagues in GTL group including Mahadi Bahari, Attili Ramkiran, Fahim Fayaz, Tan Ji Siang, Lau Ngie Jun, Shafiqah Nasir, and Sharanjit Singh Additionally, I would like to acknowledge all my lab mates, friends, and teaching staff of the Department of Chemical Engineering, College of Engineering and the Faculty of Chemical and Process Engineering Technology, Universiti Malaysia Pahang for their collaboration and friendship Finally, I dedicate this thesis to my family for their endless love, support, and the source of my motivation in pursuing the studies ii ABSTRAK Tindak balas pembaharuan kering metana (MDR) baru-baru ini muncul sebagai antara pendekatan pelbagai guna yang terbaik untuk menukar dua gas rumah hijau, karbon dioksida (CO2) dan metana (CH4), kepada bahan mentah yang berharga untuk proses hiliran petrokimia Pada masa ini, masih terdapat cabaran dalam membangunkan pemangkin yang sangat stabil dan aktif untuk tindak balas MDR di samping rintangan yang lebih baik terhadap pemendapan karbon Baru0baru ini, pemangkin berasaskan kobalt yang disokong mesopori alumina muncul sebagai pemangkin yang berpotensi Walau bagaimanapun, bahan-bahan konvensional yang digunakan untuk menyediakan sokongan pemangkin mesopori ini ialah prekursor organik dan etanol yang agak mahal dan berbahaya kepada alam sekitar Oleh itu, dalam kajian ini, penggunaan mesopori alumina (Al2O3), yang direka menggunakan prekursor aluminium bukan organik yang murah dan tersedia dalam pelarut binari etanol-air, telah dikaji sebagai sokongan untuk pemangkin kobalt Penyiasatan ini bertujuan untuk mereka bentuk sistem pemangkin berasaskan kobalt yang berkesan untuk tindak balas MDR, yang mengatasi halangan penyahaktifan yang disebabkan oleh karbon Kesan promosi La2O3 pada ciri fizikokimia pemangkin kobalt yang disokong Al2O3 dan prestasi pemangkinnya juga telah dijelaskan Penilaian mangkin dalam tindak balas MDR telah dijalankan untuk mangkin 10%Co/Al2O3 dan 10%Co/Al2O3 yang digalakkan La2O3 (pemuatan La adalah dalam 1% – 8%) dalam reaktor katil tetap pada julat suhu 923 – 1073 K dan tekanan separa bagi bahan tindak balas dari 10 hingga 40 kPa Sokongan Al2O3 mempunyai luas permukaan BET 173.4 m2 g-1 dan nanopartikel kobalt tersebar dengan halus diatas sokongan dengan saiz kristal yang dikehendaki berjulat dari 5.2 - 9.2 nm Interaksi kuat antara CoO dan Al2O3 telah disahkan dengan kehadiran spinel kobalt-aluminat dan struktur tekstur pemangkin adalah stabil terhadap suhu tindak balas Tingkah laku promosi La2O3 memudahkan pengurangan H2 dengan menyediakan ketumpatan elektron yang lebih tinggi dan meningkatkan kekosongan oksigen dalam 10%Co/Al2O3 Penambahan La2O3 boleh mengurangkan tenaga pengaktifan ketara bagi penggunaan CH4; lalu, meningkatkan penukaran CH4 sehingga 93.7% pada 1073 K Pembentukan lanthanum dioksikarbonat secara terus semasa MDR bertanggungjawab dalam pengurangan karbon termendap melalui kitaran redoks sebanyak 17-30% bergantung pada suhu tindak balas Selain itu, tahap kekosongan oksigen meningkat kepada 73.3% dengan promosi La2O3 Pemuatan 5%La ialah kandungan penggalak yang optimum untuk penukaran bahan tindak balas serta penghasilan H2 dan CO 5%La-10%Co/Al2O3 juga mempamerkan rintangan tertinggi terhadap pemendapan karbon kerana sifat asas, ciri redoks penggalak La2O3 Tindak balas MDR ke atas pemangkin 5%La-10%Co/Al2O3 telah diyakini mengikuti mod penjerapan bersekutu CH4 dan CO2 pada dwi tapak zarah aktif atau berbeza dan pemangkin menunjukkan kestabilan yang baik semasa tindak balas 48 jam pada 1023 K Nisbah H2/CO 0.84-0.98 yang terhasil adalah sesuai untuk tindak balas Fischer-Tropsch di hiliran untuk menjana bahan api hidrokarbon cecair Akibatnya, penggunaan sokongan mesopori alumina dan penggalakk La2O3 meningkatkan aktiviti Co dengan efektif dalam tindak balas MDR disamping menahan pemendapan karbon pada permukaan pemangkin iii ABSTRACT Methane dry reforming reaction (MDR) has recently emerged as a promising multipurpose approach for converting two greenhouse gasses, included carbon dioxide (CO2) and methane (CH4), into valuable feedstock for downstream petrochemical processes At present, there is still a challenge in developing the highly stable and active catalysts for MDR reaction as well as better resistance to carbon deposition Though the mesoporous alumina supported Co-based catalysts have recently appeared to be the potential catalysts However, the common starting materials for preparing these wellordered mesoporous catalyst supports are organic precursors and anhydrous ethanol which are quite expensive and harmful to the environment Therefore, in this study, mesoporous alumina (Al2O3), fabricated using a cheap and available inorganic aluminium precursor in binary water-ethanol solvent, was implemented as support for cobalt catalyst This investigation aimed to design an effective cobalt-based catalyst system for MDR reaction, which overcomes coke-related deactivation barriers The promotional effect of La2O3 on the physicochemical features of Al2O3 supported cobalt catalyst and its catalytic performance were also elucidated The catalyst evaluations in MDR reaction were conducted for 10%Co/Al2O3 and La2O3-promoted 10%Co/Al2O3 catalysts (La loading was in 1% – 8%) in a fixed-bed reactor at temperature range of 923 – 1073 K and partial pressure of individual reactant from 10 to 40 kPa The Al2O3 support has BET surface area of 173.4 m2 g-1 and cobalt nanoparticles were finely dispersed on the support with desired crystallite size ranged from 5.2 - 9.2 nm The strong interaction of CoO and Al2O3 phases was confirmed by the presence of cobalt-aluminate spinel and the textural structure of catalysts was stable with reaction temperature The promotion behavior of La2O3 facilitated H2-reduction by providing higher electron density and enhanced oxygen vacancy in 10%Co/Al2O3 The addition of La2O3 could reduce the apparent activation energy of CH4 consumption; hence, increasing CH4 conversion up to 93.7% at 1073 K Lanthanum dioxycarbonate transitional phase formed in situ during MDR was accountable for mitigating deposited carbon via redox cycle for 17-30% relying on reaction temperature Additionally, the oxygen vacancy degree increased to 73.3% with La2O3 promotion 5%La loading was an optimal promoter content for reactant conversions as well as yield of H2 and CO 5%La-10%Co/Al2O3 also exhibited the highest resistance to carbon deposition owing to the basic nature, redox feature of La2O3 dopant The MDR reaction over 5%La-10%Co/Al2O3 catalyst was convinced to follow an associative adsorption mode of CH4 and CO2 on dual or different sites of active particles and the catalyst exhibited a good stability during 48 h reaction at 1023 K The resulting H2/CO ratios of 0.84-0.98 are suitable for Fischer-Tropsch reaction in downstream to generate liquid hydrocarbon fuels As a result, the employment of mesoporous alumina support and La2O3 promoter efficiently boosted the Co activity in MDR reaction along with suppressing the carbon deposition on the catalyst surface iv TABLE OF CONTENT DECLARATION TITLE PAGE ACKNOWLEDGEMENTS ii ABSTRAK iii ABSTRACT iv TABLE OF CONTENT v LIST OF TABLES ix LIST OF FIGURES x LIST OF ABBREVIATIONS xv CHAPTER INTRODUCTION 1.1 Research Background 1.2 Motivation 1.3 Problem Statements 1.4 Objectives of Study 1.5 Scope of Study 1.6 Thesis Organization CHAPTER LITERATURE REVIEW 2.1 Introduction 2.2 Overview of Syngas 2.3 Methane Dry Reforming Reaction 11 2.3.1 11 The Kinetics Studies v 2.4 2.3.2 Catalyst Deactivation 18 2.3.3 The Catalyst Development 22 Concluding Remarks 40 CHAPTER METHODOLOGY 41 3.1 Introduction 41 3.2 Materials and Equipment 43 3.3 Catalyst Preparation 45 3.3.1 Alumina Support 45 3.3.2 Catalyst 45 3.4 3.5 3.6 Catalyst Characterization 46 3.4.1 Textural Analyses 46 3.4.2 X-ray Diffraction Analysis 47 3.4.3 H2 Temperature-programmed Reduction 48 3.4.4 CO2 Temperature Programmed Desorption 48 3.4.5 Temperature-programmed Oxidation 49 3.4.6 High Resolution Transmission Electron Microscopy 49 3.4.7 Raman Spectroscopy 49 3.4.8 X-ray Photoelectron Spectroscopy 50 Catalyst Evaluation 50 3.5.1 Experimental Set-up 50 3.5.2 Product Analysis 52 3.5.3 Mass Flow Controller Calibration 52 3.5.4 Transport Resistance Estimation 53 Kinetic Parameters Determination and Modelling vi 54 Figure 5.21 Carbon formation on spent 10%Co/Al2O3 and 3%La-10%Co/Al2O3 after MDR at 973 K, 1023 K, and 1073 K and feed ratio of As seen in Figure 5.21, the amount of carbons on spent 3%La-10%Co/Al2O3 was always less than that of spent 10%Co/Al2O3 about 17-30% depending on temperature The positive effect of La2O3 promotion was accounted for the reduction in carbon deposition Indeed, the basic nature of La2O3 could attract more CO2 adsorption for gasifying surface CxHy carbonaceous species (Bahari et al., 2017) In addition, the smaller crystalline size of 3%La-10%Co/Al2O3 was allegedly responsible for carbon resistance (Usman et al., 2015) The oxidation of carbonaceous materials on promoted catalyst surface was also associated with the high oxygen mobility and redox character of La2O3 (Kang Li et al., 2019) The great oxygen storage capacity of La2O3 could induce the formation of lanthanum dioxycarbonate (La2O2CO3) transitional phase via the reaction between La2O3 and CO2 This intermediate form could subsequently eliminate CxHy species from the catalyst surface as illustrated in Figure 5.22 97 Figure 5.22 La2O3 redox cycle for surface carbon removal during MDR The effect of La-loadings on the amount of accumulated carbon in La2O3-promoted catalysts after MDR reaction at 1023 K was accessed through TPO measurements and shown in Figure 5.23 Like Raman results (see Figure 5.20), two distinguished peaks P1 and P2 appearing in the derivative weight plots of promoted and unpromoted samples, were assigned to amorphous and graphitic carbons oxidation, respectively The promotion of La2O3 shifted peak P1 to a lower temperature zone and lessened the intensity of peak P2 This observation suggests the enhanced reactiveness of amorphous carbon and reducing graphite formation on promoted catalysts in line with other studies (Fayaz et al., 2019) As seen in the inset of Figure 5.23, the presence of La2O3 promoter reduced the amount of accumulated carbon from 47.7% (10%Co/Al2O3) to 34.6% (5%La-10%Co/Al2O3) The reduction in carbon deposit could be due to the increasing basic site density on La2O3-promoted catalyst (see Figure 5.4), facilitating the likely or potential formation of La2O2CO3 intermediate phase from La2O3 and CO2 interaction (see Figure 5.24) (Charisiou et al., 2019) This intermediate phase could further oxidize the carbonaceous species from the catalyst surface to maintain catalytic activity (Fayaz et al., 2019) 98 Figure 5.23 Derivative weight TPO profiles of selected spent 10%Co/Al2O3, 3%La10%Co/Al2O3, 5%La-10%Co/Al2O3, and 8%La-10%Co/Al2O3 after MDR at 1023 K and feed ratio of Figure 5.24 Mechanism for carbonaceous deposition removal from catalyst surface with the assistance of La2O3 promoter 99 As illustrated in Figure 5.25, the yield of CO and H2 exponentially decreased with the rising carbon formation rate, which was calculated based on time average The exponential decay in CH4 and CO2 conversions was also observed when the carbon formation rate increased from 1.8410-5 to 3.1710-5 gcarbon gcat-1 s-1 This relationship convincingly confirms that deposited carbon formation rate is the main factor adversely affecting the catalytic MDR performance as Co0 active site was surrounded by deposit carbon Figure 5.25 The correlation between catalyst performance and carbon formation rate 5.4.4 X-ray Photoelectron Analyses The XPS scans were conducted for selected spent samples to examine the surface oxidation states and carbonaceous types The binding energy (BE) in all spectra was adjusted based on the C 1s peak of adventitious carbon at 284.6 eV The XPS narrow scan spectra for Co 2p3/2, C 1s, La 3d and O 1s are displayed in Figure 5.26, Figure 5.27, Figure 5.28 and Figure 5.29, respectively whilst the interpretation of binding energy is summarized in Table 5.5 100 Table 5.5 1023 K XPS peak Summary of XPS peaks assignments for spent catalysts after MDR at Binding energy (eV) Co 2p3/2 Assignment Ref (Álvarez-Docio, Reinosa, Del Campo, & Fernández, 2019) (Álvarez-Docio et al., 2019) 10%Co/Al2O3 3%La‐ 10%Co/Al2O3 786.5 786.4 Satellite peak 782.2 781.4 CoAl2O4 780.4 779.6 Co3O4 (Paksoy, Caglayan, & Aksoylu, 2015) 778.9 778.0 Co (0) (Paksoy et al., 2015) 285.7 285.6 Amorphous carbon 284.6 284.6 Graphitic carbon 531.5 531.0 Adsorbed oxygen species (Ewbank, Kovarik, Kenvin, & Sievers, 2014; Long et al., 2011) (Cui, Zhang, Lin, & Wang, 2016; Ewbank et al., 2014) (Y Chen et al., 2017; Fayaz et al., 2019) C 1s Surface lattice oxygen in Al2O3 and/or Co3O4 O 1s 529.7 529.6 La 3d3/2 - 851.9 La 3d5/2 - 835.1 La2O2CO3 (Y Chen et al., 2017; Fayaz et al., 2019) (G Chen, Han, Deng, Wang, & Wang, 2014) Figure 5.26 shows that the expanded Co 2p3/2 spectra of spent catalysts were deconvoluted into four peaks using Gaussian algorithm in Origin Pro 2016 software As summarized in Table 5.5, the Gaussian peaks were observed at BEs of 778.0-778.9, 779.6780.4, 781.4-782.2 and 786.4-786.5 eV, belonging to the metallic Co0, Co3O4 oxide, CoAl2O4 spinel phases and a satellite shake‐up band in this order (Álvarez-Docio et al., 2019; Paksoy et al., 2015) The co-existence of various Co and Co oxide species is in line with XRD results (Figure 5.2) It is noteworthy to mention that all cleaved peaks of Co 2p3/2 narrow scan on La2O3-promoted specimen located at lower BE values than those of the unpromoted 101 counterpart This could confirm the enriched electron density over cobalt particles induced by electron-donating La2O3 promoter (Fayaz et al., 2019; Q Guo et al., 2018) Hence, the electron-rich environment on 3%La‐10%Co/Al2O3 alleviated the H2 reduction process as aforementioned in H2-TPR (Figure 5.3) Figure 5.26 Co 2p3/2 XPS spectra for spent (a) 10%Co/Al2O3 and (b) 3%La10%Co/Al2O3 after MDR at 1023 K and feed ratio of The enlarged C 1s XPS spectra (Figure 5.27) demonstrated the co-presence of graphitic carbon and amorphous carbon in line with the above-mentioned Raman results (i.e., G-band and D-band, respectively, as given in Figure 5.19) In particular, the peak at BE of 284.6 eV was assigned to graphitic carbon whilst amorphous carbon was depicted with the broad BE signal at around 286 eV (L Liu, Ma, & Li, 2014; X Zhao, Zhu, & Yang, 2014) 102 Figure 5.27 C s XPS spectra for spent (a) 10%Co/Al2O3 and (b) 3%La-10%Co/Al2O3 after MDR at 1023 K and feed ratio of Interestingly, the La 3d XPS detailed scan of spent 3%La‐10%Co/Al2O3 (see Figure 5.28) revealed two doublet peaks with BE gap of about 16.8 eV typical value for La3+ (G Chen et al., 2014) These doublet peaks correspond to La 3d3/2 (BE of 851.9 eV) and La 3d5/2 (BE of 835.1 eV) belonging to lattice lanthanum in intermediate La2O2CO3 form on catalyst surface (G Chen et al., 2014) The detection of this intermediate phase formed by La2O3 and CO2 reaction would convincingly prove the simultaneous carbon gasification in MDR through the in situ redox and oxidation cycle of La2O2CO3 ↔ La2O3 as illustrated in Figure 5.22 It is noteworthy to mention that, unlike XPS analysis, the XRD pattern of spent La2O3promoted 10%Co/Al2O3 can not identify the formation of lanthanum dioxycarbonate possessing the characteristic diffraction peaks at 2 : 13.1o, 22.8o, 29.6o, 30.8o, 41.1o and 44.5o (JCPDS card No 22-1127) (Kalai, Stangeland, Jin, Tucho, & Yu, 2018) It could be assigned to the low sensitivity of XRD measurement induced by small La2O2CO3 crystallite size and low La loading 103 Figure 5.28 La 3d XPS spectrum for spent 3%La-10%Co/Al2O3 after MDR at 1023 K and feed ratio of The mobile oxygen vacancy of catalysts is a key factor determining the degree of carbon removal from the catalyst surface as it is the preferred site for the adsorption of CO2 oxidizing agent The mobile oxygen vacancy was evaluated based on the O 1s XPS signal as shown in Figure 5.29 The surface lattice oxygen atoms from Co3O4 and Al2O3 forms were detected at BE around 529.6 - 529.7 eV (peak II), whilst the deconvoluted peak I at 531.0 531.5 eV matched to the surface adsorbed oxygen species in carbonate compounds induced by oxygen vacancies in catalysts (Zhou et al., 2018) Hence, the degree of oxygen vacancies, DO-Vac (%) could be quantified via the relative amount of adsorbed oxygen in spent catalysts as expressed in Equation 5.10 (N Wang et al., 2013) DO Vac (%)  OAds 100% (OLat  OAds ) 5.10 where OAds and OLat , in turn, belong to the integral areas of peaks I and II (Figure 5.29) 104 The oxygen vacancy degree of spent 3%La-10%Co/Al2O3 was about 73.3%, which was 1.4 times higher than that of the spent unpromoted counterpart (51.8%) Interestingly, the increasing DO-Vac value of 1.4 times with La2O3 addition was also close to the magnification of decreasing carbon deposition (up to 1.3 times) This further confirms that La2O3 promotion hindered carbonaceous deposits, and oxygen vacancy degree was one of the main factors responsible for surface carbon removal Figure 5.29 O 1s XPS spectra for spent (a) 10%Co/Al2O3 and (b) 3%La-10%Co/Al2O3 after MDR at 1023 K and feed ratio of 5.4.5 HRTEM Surface Morphology Study The HRTEM analyses of fresh and spent catalysts are presented in Figure 5.30 The relatively uniform feature of Al2O3 support was apparently evident for both fresh catalysts, and the Al2O3 mesoporous were adhered together as seen in Figure 5.30(a) and (b) The tiny and dark spots labelled with yellow circles (Figure 5.30(a)) could demonstrate the presence of Co nanoparticles Interestingly, these nanoparticles were randomly dispersed on the catalyst surface without agglomeration, although catalysts were previously calcined at high temperature of 873 K The thermal agglomeration resistance could be due to the strong interaction between Al2O3 support and Co metal Thus, it could impede the movement of Co nanocrystals to form large particles under thermal treatment The absence of un-favoured metal accumulation could also contribute to result in a great catalytic activity with reactant conversions of more than 90% in this work As seen in Figure 5.30(c) and Figure 5.30(d), the 105 unavoidable amorphous carbon and graphite were clearly spotted on spent catalysts corroborated with Raman (Figure 5.19) and XPS (Figure 5.27) results because of thermally preferred CH4 decomposition in agreement with other studies (Charisiou et al., 2019) Notably, the size of cobalt particles presented in both spent catalysts patterns was estimated less than 10 nm which could be due to the confinement effect of mesoporous Al2O3 support preventing the active metal agglomeration These observations further consolidated the positive contributions of Al2O3 support on enhancing the cobalt catalyst performance on MDR reaction in term of its activity and stability (a) (b) Co Al2O3 (d) (c) Amorphous C Amorphous C Graphite 100 nm Figure 5.30 HRTEM images of (a) fresh 10%Co/Al2O3, (b) fresh 3%La10%Co/Al2O3, (c) spent 10%Co/Al2O3, and (d) spent 3%La-10%Co/Al2O3 after MDR at 1023 K and feed ratio of 106 In conclusion, the noble and non-noble based catalysts applied in MDR are shown in Table 5.6, the 5%La-10%Co/Al2O3 catalyst in this study possessed the low degree of catalyst deactivation rate of about 0.03% h-1 for CH4 Additionally, 5%La-10%Co/Al2O3 catalyst exhibited a comparable CH4 conversion to those of noble-base catalysts after h on-stream reaction runs (Aramouni et al., 2020; Da Fonseca et al., 2020; Ma et al., 2016) From the above observation, 5%La-10%Co/Al2O3 catalyst seems to be a promising catalyst with high catalytic activity and stability for industrial application of MDR The outstanding performance of 5%La-10%Co/Al2O3 catalyst in comparison with other promoted and unpromoted Co-based catalysts could be assigned to the promotional effect of La2O3 addition The addition of La2O3 not only effectively hindered the graphitic carbon formation but also retained the reactiveness of filamentous carbon and hence facilitating the CO2 gasification of deposited carbon on catalyst surface Thus, La2O3 promotion could restore the active sites of metallic Co0 phase and maintain the high catalytic activity with time-onstream 107 Table 5.6 Summary of MDR performance over different catalysts reported in literature Textural properties Catalyst XCH₄ (%) H2:CO ratio 24 67 0.90 (Da Fonseca et al., 2020) Reaction conditions Refs SBET (m2g-1) Vp (cm3g-1) Dp (nm) dM* (nm) T (K) 118 n.m n.m n.m 1073 GHSV (L gcat-1 h1 ) n.m 129.6 0.45 13.9 9.4 1073 11 45 96 n.m (Aramouni et al., 2020) 282 0.605 8.42 - 1023 24 n.m 86 n.m 10%Ni/ZrO2 193 0.31 5.0 7.3 1023 24 10 60 n.m 7%Ni/ZSM-5 250 - - - 1073 60 12 66 n.m (Ma et al., 2016) (X Zhang, Zhang, Tsubaki, Tan, & Han, 2015) (Estephane et al., 2015) 5%Ni/NYZ 14.83 0.084 n.m 17.4 973 24 0.5 72 0.91 (M Zhang et al., 2020) 0.8Co-Ni/CeO2 11.94 0.28 3.80 31.34 1073 12 10 77 0.90 (Turap et al., 2020) NiY4/DLH 153 0.7 18 4.0 973 20 84 1.00 (Świrk et al., 2021) 10%Ni/CeAl 144 0.35 7.1 11.3 1073 27 24 93 0.95 (Marinho et al., 2021) 10%Ni/SBA-15 538.6 0.89 6.64 14.5 1073 36 62 n.m (S Singh, Bahari, et al., 2018) 10%Co/SBA-15 628 1.3 7.22 11.5 973 1.2 24 0.34 (Taherian et al., 2017) 20%Co/La2O3 16.45 0.0113 1.22 6.99 1023 15 n.m 49 n.m (Ayodele, Khan, Lam, et al., 2016) 10%Co/Y Zeolite 262.7 - - 13.9 1123 24 10 79.7 0.78 (Abdollahifar et al., 2015) 20%Co/Nd2O3 18.67 0.0061 1.19 27.5 1023 15 n.m 63.5 n.m (Ayodele, Hossain, et al., 2016) 20%Co/CeO2 39.35 0.0141 1.16 - 1023 15 72 1.30 (Ayodele, Khan, & Cheng, 2016) Pt/CePr/Al2O3 Ni-Co-Ru/neutral SGM 0.5%Pd6%Ni/Al2O3 108 TOS (h) Table 5.6 Continued Textural properties Catalyst SBET (m2g-1) Vp (cm3g-1) Dp (nm) 10%Co/Al2O3# 203.9 0.70 3%Y10%Co/Al2O3# 155.8 20%Co/Nd2O3 10%Co/Al2O3 (Commercial support)@ 10%Co/Al2O3 5%La10%Co/Al2O3 Reaction conditions dCob XCH₄ (%) H2:CO ratio Refs (nm) T (K) GHSV (L gcat-1 h1 ) TOS (h) 15.3 12.9 1023 36 70.9 1.05 (Bahari, Setiabudi, Nguyen, Jalil, et al., 2020) 0.52 14.8 12.7 1023 36 85 0.95 (Bahari et al., 2021) 18.67 0.0061 1.19 27.5 1023 15 n.m 63.5 n.m (Ayodele, Hossain, et al., 2016) 143.09 0.36 10.7 14.05 1023 36 56.3 0.83 This study 973 36 47.5 0.63 This study 1023 36 70.0 0.84 This study 1073 36 76.2 0.89 This study 973 36 75.8 0.84 This study 1023 36 90.5 0.98 This study 1073 36 93.5 0.99 This study ® 141.9 123.6 0.22 0.18 6.28 5.90 9.2 8.0 * Partical size of active metal calculated from Scherrer equation Mesoporous γ-Al2O3 support prepared by Self-assembly hydrothermal-assisted (SAHA) using aluminum isopropoxide precusor @ Calcined γ-Al2O3 support (Puralox SCCa-150/200) obtained from Sasol # 109 5.5 Concluding Remarks The functional effect of La2O3 promoter and its loading on the physicochemical features of La2O3-promoted 10%Co/Al2O3 catalyst as well as its performance for MDR reaction were investigated The addition of La2O3 nanoparticles did not substantially distort the mesoporous structure of Al2O3 support In contrast, both Co and La metal oxides were well distributed on Al2O3 surface with small Co3O4 crystal size within 5.2-8.4 nm The alleviated reduction process (for Co3O4 → CoO) and increasing basic site concentration of catalyst were clearly evident with La2O3 incorporation The MDR using CH4/CO2 = 1:1 and 1023 K showed that the rising basic site concentration and lowering active metal crystallite size associated with La2O3 promotion improved the conversion of CH4 and CO2 toward 29.3% and 17.3%, correspondingly The promotion of La2O3 significantly suppressed carbon deposition from 47.7% to 34.6% owing to the basic feature of promoter and the formed La2O2CO3 intermediate phase simultaneously removing surface carbonaceous species from catalyst surface during MDR Amongst promoted catalysts, 5%La-10%Co/Al2O3 was the best catalyst in terms of carbon resistance, yields of CO and H2 The MDR performed over 5%La-10%Co/Al2O3 catalyst follows dual-site associative adsorption of CH4 and CO2 with bimolecular surface reaction, while catalyst appealed good stability for 48 h with insignificant drops of conversions rate of CO2 (0.05% h-1) and CH4 (0.03% h-1) The resulting H2/CO ratios of 0.84-0.98 are suitable for Fischer-Tropsch reaction in downstream to generate liquid hydrocarbon fuels 110 CHAPTER CONCLUSIONS AND RECOMMENDATIONS 6.1 Conclusions Methane dry reforming has been considered as a promising alternative approach for syngas generation This process produces syngas with a preferred H2/CO ratio for downstream petrochemical industries The objectives of this study have been achieved to a large extent and the outcomes for MDR evaluation over La2O3-promoted and unpromoted 10%Co/Al2O3 catalysts are summarized as follow: Mesoporous alumina was successfully synthesized via the EISA method using an inorganic aluminum nitrate nonahydrate precursor in a mixed solvent of waterethanol solution All promoted and unpromoted cobalt catalysts on mesoporous Al2O3 support displayed a typical type-IV isotherm and H1 shaped hysteresis loop which are typical features of mesoporous materials with the cylindrical pore geometry The addition of La2O3 nanoparticles did not substantially distort the mesoporous structure of Al2O3 support In contrast, both Co and La metal oxides were well distributed on Al2O3 surface with small Co3O4 crystal size within 5.2-8.4 nm The alleviated reduction process (for Co3O4 → CoO) and increasing basic site concentration of catalyst were clear with La2O3 incorporation The functional effect of La2O3 promoter and its loading on the physicochemical features of La2O3-promoted 10%Co/Al2O3 catalyst as well as its performance for MDR reaction were investigated The MDR over La2O3-promoted 10%Co/Al2O3 catalyst with various La loading using CH4/CO2 = 1:1 and 1023 K showed that the rising basic site concentration and lowering active metal crystallite size associated with La2O3 promotion improved the conversion of CH4 and CO2 toward 29.3% and 17.3%, correspondingly The promotion of La2O3 significantly suppressed carbon deposition from 47.7% to 34.6% owing to the basic feature of promoter and formed La2O2CO3 intermediate phase simultaneously removing surface carbonaceous species from catalyst surface during MDR Amongst promoted catalysts, 5%La111