Syngas Production from Catalytic CO2 Reforming of CH4 over CaFe2O4 Supported Ni and Co Catalysts: Full Factorial Design Screening

In this study, the potential of dry reforming reaction over CaFe2O4 supported Ni and Co catalysts were investigated. The Co/CaFe2O4 and Ni/CaFe2O4 catalysts were synthesized using wet impregnation method by varying the metal loading from 5-15 %. The synthesized catalysts were tested in methane dry reforming reaction at atmospheric pressure and reaction temperature ranged 700-800 oC. The catalytic performance of the catalysts based on the initial screening is ranked as 5%Co/CaFe2O4 < 10%Co/CaFe2O4 < 5%Ni/CaFe2O4 < 10%Ni/CaFe2O4 according to their performance. The Ni/CaFe2O4 catalyst was selected for further investigation using full factorial design of experiment. The interaction effects of three factors namely metal loading (5-15 %), feed ratio (0.4-1.0), and reaction temperature (700-800 oC) were evaluated on the catalytic activity in terms of CH4 and CO2 conversion as well as H2 and CO yield. The interaction between the factors showed significant effects on the catalyst performance at metal loading, feed ratio and reaction temperature of 15 %, 1.0, and 800 oC. respectively. The 15 wt% Ni/CaFe2O4 was subsequently characterized by Thermogravimetric (TGA), X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), N2-physisorption, Temperature Programmed Desorption (TPD)-NH3, TPD-CO2, and Fourier Transform Infra Red (FTIR) to ascertain its physiochemical properties. This study demonstrated that the CaFe2O4 supported Ni catalyst has a good potential to be used for syngas production via methane dry reforming. Copyright © 2018 BCREC Group. All rights reserved


Introduction
The mitigation of greenhouse gases such as CH4 and CO2 which contribute about 72 % and 7 %, respectively, to "greenhouse effect" has attracted growing interest in the last one decade [1].Several methods such as carbon capture and storage, energy efficiency and conservation, negative CO2 emission and catalytic reforming of methane have been explored to mitigate greenhouse effect [2][3][4].Among these options, that noble metals are typically much more carbon resistant compared to Co and Ni-based catalyst in methane dry reforming but are expensive and might not be economical for scale up.On the contrary, Co and Ni-based catalysts are inexpensive and show comparable activity with the noble metals [11,12].The catalytic performance of Co-and Ni-based can be enhanced using suitable supports.Supports such as Al2O3, CeO2, SiO2, and MgO have been widely explored for the synthesis of Co and Nicatalysts [13][14][15][16].These catalysts showed various degrees of catalytic performance.However, extensive literature search has shown that CaFe2O4 which has good acidicity and basicity properties has only been used as catalysts in processes such as photo-degradation of methylene blue as well as in biodiesel production [17,18].To the best of the authors' knowledge, there is presently no literature on the use of CaFe2O4 as support for synthesis of Co-and Nibased catalyst for methane dry reforming.Therefore, the aim of this study was to investigate the initial screening of Co and Ni supported on CaFe2O4 for methane dry reforming.The best performing catalyst in terms of the reactants conversion and products yields was subsequently characterized using different instruments techniques, such as: TGA, XRD, EDX, XPS, N2 physisorption, and FTIR, to establish its physiochemical properties.To further explore its potential as dry reforming catalyst, a further screening of the catalyst was performed using full factorial design by consid-ering factors such as metal loadings, feed (CH4: CO2) ratio and reaction temperature.

Synthesis of catalysts
Prior to the synthesis of the Co-and Ni/CaFe2O4 catalysts, the CaFe2O4 support was prepared by sol-gel technique reported elsewhere [17].In a typical synthesis, a stoichiometric ratio of Ca(NO3)2.4H2Oand Fe(NO3)3.9H2Owere mixed in 30 % aqueous NH3 solution, and the mixture was stirred at room temperature for 24 h.The solution was then slowly heated to 80 o C and maintained at that temperature level until the water evaporated.The resulting brown dry gel-like slurry was calcined at 450 o C for 2 h followed by heat treatment at 900 o C for 10 h using muffle furnace to obtained CaFe2O4 powder.Finally, CaFe2O4 powders were crushed in the mortar to obtain fine particle size.Thereafter, Ni/CaF2O4 was synthesized with metal loading of 5-15 wt% using wet-impregnation method.Required amount of Ni(NO3)2.6H2Oprecursor was dissolved in aqueous solution and 1 g of CaFe2O4 was added to the solution under stirring for 3 h.Subsequently, the slurry was oven dried for 24 h at 120 o C, crushed and finally calcined at 800 o C for 5 h.Similarly, Co/CaFe2O4 with metal loading of 5-10 wt% was synthesized using the same method mentioned above.The Co(NO3)2.6H2O was used as precursor for this purpose.All the reagents were analytical grade (99.99 % purity, Sigma-Aldrich, USA) and were used as received without further purification.

Pre-screening of the Co/CaFe2O4 and Ni/CaFe2O4 catalysts
Prior to the full factorial design of experiment, a preliminary experiment was carried out to determine a promising active element from Co and Ni that can be synthesized on the CaFe2O4 support.The Ni/CaFe2O4 catalyst was selected for further screening based on its activity in terms of conversion and yield.A full factorial design of the Ni/CaFe2O4 was performed using Statistica 13 software (Dell incorp.)for the design of experiment.The effect of factors such as metal loading (5-15 %), feed ratio (0.4-1) and reaction temperature (700-800 o C) on the CH4 and CO2 conversion as well as the H2 and CO yield.The full factorial design of the Ni/ CaFe2O4 is depicted in Table 1.

Catalyst characterization
The catalyst (15%wt Ni/CaFe2O4) with the best performance was further characterized for its physicochemical properties using different instrument techniques.The thermal analysis showing the changes in the physical and chemical properties of the 15%wt Ni/CaFe2O4 catalyst as a function of increasing temperature was done using Hitachi simultaneous thermal analyser (STA, 7000 series).The STA has the capacity to simultaneously perform Thermogravimetric Analysis (TGA) and Differential Thermal Analysis (DTA).The uncalcined catalyst sample weighing approximately 6 mg was placed in an alumina pan enclosed in a furnace.The temperature of the furnace was increased from 25 to 900 o C at heating rate of 10 o C/min in a flow of 50 mL/min of pure N2.The weight loss (TG) and the differential weight loss (DTG) of the catalyst sample as a function of temperature were estimated.The texture properties of the calcined 15%wt Ni/CaFe2O4 catalyst in terms of BET specific surface area and BJH pore size distribution were measured by N2 physisorption method using Accelerated Surface Area and Porosimetric system (ASAP 2020 plus).The catalyst sample was degassed at 253 o C for 2 h before the commencement of the N2 physisorption analysis.The 15wt% Ni/CaFe2O4 catalyst was characterized for phase identification by X-ray powder diffraction analysis using RIGAKU miniflex II X-ray diffractometer.The XPS analysis was performed using Thermo Fisher K-alpha equipped with monochromatic Al Kα X-ray source.The XPS spectra were collected using aluminium anode (Al-Kα =1486.6 eV) operating at 150 W. The recording of the spectra was done at background pressure of 2 × 10 -9 mbar under an ultra-high vacuum (UHV) chamber.The TPD analysis using NH3 and CO2 as probing gases were carried out using approximately 60 mg each of the fresh catalyst.Prior to the testing the catalyst was pretreated in a flow of 20 mL min -1 N2 for 1 h at a heating rate of 10 o C min -1 up to 50 o C at holding time of 30 min.The pre-treated catalyst sample was thereafter purged with He and then cooled down to room temperature.The TPD-NH3 analysis was done by replacing the He gas with NH3 and allowed to saturate the samples for 1 h.This was followed by purging the sample with He to remove either excess NH3 in gas phase or the physisorbed NH3 on the catalysts.The desorption step was carried out under 20 mL min -1 He flows at a heating rate of 20 o C min -1 from room temperature to 900 o C and holding time of 20 min before cooling.The amount of NH3 desorbed was estimated from the TPD pattern recorded online.The above procedure was repeated for TPD-CO2 analysis using CO2 gas in place of the NH3 gas.

Catalytic activity test
The schematic diagram of the experimental set-up for the catalytic activity test is represented in Figure 1.The set-up comprised CO2, CH4, N2 and H2 gases (99.99 % purity).The main reactants for the methane dry reforming are CO2 and CH4, while N2 and H2 serve as carrier gas and for reduction, respectively.The stainless steel fixed bed continuous reactor was packed with 200 mg of catalysts supported with quartz wool and heated inside a split-tube furnace that was equipped with K-type thermocouple for measurement of the catalytic bed temperature.The catalyst was reduced in 60 mL/min of 20 % H2 and 80 % N2 prior to the commencement of the catalytic activity test at 900 o C for 1 h.The flow rate of the inlet gas was maintained at 100 mL/min and individually regulated with the aid of Alicat digital mass flow controller (MFC) (Alicat Scientific Inc., USA).The outlet gas composition (CO2, CH4, CO and H2) was measured with gas chromatography (GC) instrument (Agilent Technologies, USA) equipped with thermal conductivity detector (TCD).Two packed columns were used viz.Supelco Molecular Sieve 13x (

Bulletin of Chemical Reaction Engineering & Catalysis, 13 (1), 2018, 61
Copyright © 2018, BCREC, ISSN 1978-2993 H2, CH4 and CO2 were performed using Hayesep DB column; whilst CO were analysed using the Molecular Sieve 13× columns.The conversion of CH4 and CO2 as well as the yields of H2 and CO were calculated using Equations ( 2)-( 5). ( where FCO2in, FCH4in, FCO2out, and FCH4out are the inlet and outlet molar flow rates of CO2 and CH4, respectively.FH2 and FCO are the outlet molar flow rates of H2 and CO, respectively.

Pre-screening of the Co-and Ni/CaFe2O4 catalysts
The pre-screening of the catalyst for dry reforming of methane was performed over the two selected active metals, Co-and Nisupported on CaFe2O4 in order to determine which of the active metals can further be selected for subsequent full factorial design.In addition, the catalyst activity of the CaFe2O4 support was also tested.The pre-screening experiments were carried out considering factors, such as metal loadings (5-10 %), feed ratio (CH4/CO2) (0.4-1) and reaction temperature (700-800 o C).The performance of the catalysts was measured based on the conversions of the CH4 and CO2 as well as the yields of H2 and CO.The feed flowrate was fixed at GHSV of 30000 h -1 .The activities of the CaFe2O4 support and the catalysts are shown in Figure 2(a)-(d).It can be seen that CaFe2O4 shows some activities in term of reaction conversions and the products yields (Figure 2 (a)).The highest values of 16.4 % and 6.8 % were obtained for CH4 and CO2 conversions while 13.7 % and 14.10 % were obtained for the H2 and CO yield respectively at feed (CH4:CO2) ratio of and temperature of 800 o C.This implies that the CaFe2O4 plays significant role in the catalytic activities of the Co and Ni catalysts.The catalysts show an increasing trend with reaction temperature in terms of CH4 and CO2 conversions.
Figure 2 (b)-(d) revealed that, CH4 and CO2 conversions did not vary much with the metal loading using the Co/CaFe2O4.This is evident in the overlapping trend obtained for the CH4 and CO2 conversions using 5% Co/CaFe2O4 and 10% Co/CaFe2O4 catalysts.On the contrary, CH4 and CO2 conversions increased with metal loadings and temperature using the Ni/CaFe2O4.Similar, trends can also be observed in terms of H2 and CO yields.Hence, the catalytic performance for the pre-screening experiment can be ranked as 5% Co/CaFe2O4 < 10% Co/CaFe2O4 < 5% Ni/CaFe2O4 < 10% Ni/CaFe2O4 based on their activities in terms of yield and conversion.Based on the performance of the two-screened catalyst, Ni/CaFe2O4 catalyst was selected for full factorial design of experiment.

Catalytic performance of Ni/CaFe2O4 catalyst
The catalytic performance of the 5% Ni/CaFe2O4, 10% Ni/CaFe2O4 and 15% Ni/CaFe2O4 catalysts are depicted in Figures 3-5.Generally, the CH4 and CO2 conversion as well as the H2 and CO yield showed increasing trend with feed ratio and reaction temperature.The catalytic performance of 5% Ni/CaFe2O4 is depicted in Figure 3.It can be seen that there was slight increase in the CH4 conversion from 700-800 o C at feed ratio of 0.4 and 0.7 (cf. Figure 3 (a)).However, the CH4 conversion drastically increased with temperature at unity feed ratio.On the contrary, CO2 conversion significantly increased with the reaction temperature and feed ratio (cf. Figure 3 (b)).Highest values of 50.7 % and 47.6 % were obtained for the CH4 and CO2 conversions at reaction temperature and feed ratio of 800 o C and 1.0, respectively.The higher value of CH4 conversion obtained could be as result of side reaction such as methane cracking [19].Furthermore, both the H2 and CO yields increased with reaction temperature and feed ratio as shown in Figures 3 (c Furthermore, the catalytic activity of the 10% Ni/CaFe2O4 catalyst is shown in Figure 4.The catalyst also displayed impressive activity in terms of CH4 and CO2 conversion as well as H2 and CO yield.It is noteworthy that the CH4 conversion increases with both feed ratio and temperature.Similarly, CO2 conversion also increases with feed ratio and temperature.However, the increase in the CH4 conversion was not pronounced at temperature of 700 and 800 o C using feed ratio of 0.4.The methane dry reforming over 10% Ni/CaFe2O4 demonstrated highest CH4 and CO2 conversions of 67.97 and 66.38%, respectively, which was higher compared to the performance of 5% Ni/CaFe2O4.The lower CO2 conversion obtained over 10% Ni/CaFe2O4 might be due to the possibility of influence of side reaction such as methane cracking which leads to higher conversion of CH4.The 10% Ni/CaFe2O4 catalyst also show an interesting performance in terms of the yield of the products (H2 and CO).Both the H2 and CO yield increases with feed ratio and temperature.
The methane dry reforming reaction over the 10% Ni/CaFe2O4 catalyst gave highest H2 and CO yields of 35.34 % and 38.31 %, respectively at feed ratio of 1.0 and temperature of 800 o C. The higher values of CO yield obtained compare to that of H2 indicate the possibility of the influence of reverse Boudouard reaction which increases the yield of the CO in addition to the product obtained from the dry reforming reaction.
The catalytic performance of 15% Ni/CaFe2O4 catalysts in methane dry reforming is depicted in Figure 5.The catalysts showed an interesting activity in terms of CH4 and CO2 conversion as well as H2 and CO yield.The CH4 conversion using feed ratio of 0.4 showed slight increase in the temperature range of 700-800 o C.However, the increase in the CH4 conversion with the temperature became pronounced at feed ratio ranged 0.7-1.0.
The catalytic activity resulted to highest CH4 conversion of 90.04 % at feed ratio of 1.0 and temperature of 800 o C. Similarly, CO2 conversion also increases with reaction temperature and feed ratio resulting to highest conversion of 87.60 % which is lower compared to that of CH4.The lower conversion of CO2 obtained implies that there might be possibility of influence of side reaction, such as methane cracking, which leads to higher conversion of CH4 [20].The highest values of CH4 and CO2 conversions obtained for the 15% Ni/CaFe2O4 catalyst is this study is comparable with conversion values of ~91 % and ~92 % obtained for CH4 and CO2 by Du et al. [21] using Ni/CeO2 catalyst.The CH4 and CO2 conversions obtained in this study is higher than 78 % and 60 % reported by Sutthiumporn [22] using alkaline promoted Ni/La2O3 catalyst.The variation in the catalytic performance could be as a result of the difference in the catalysts physicochemical properties.The 15% Ni/CaFe2O4 catalyst also shows an interesting performance in terms of the yield of the products (H2 and CO).Both the H2 and CO yields increase with feed ratio and temperature.
The catalytic activity of the 15% Ni/CaFe2O4 catalyst gives highest H2 and CO yields of 73.41 % and 74.43 % respectively at feed ratio of 1.0 and temperature of 800 o C. The higher values of CO yield obtained compare to that of H2 indicated the possibility of the influence of reverse Boudouard reaction which increases the yield of the CO in addition to the product obtained from the dry reforming reaction [23].

Catalyst characterization
The thermal analysis profile of the uncalcined 15%wt Ni/CaFe2O4 catalyst is depicted in Figure 6.Typically, the temperature pro-  The XPS spectra and the plot of the atomic concentration showing the oxidation state and the elemental composition of the catalyst are depicted in Figure 9 (a) and (b), respectively.It can be seen that all the elemental components such as Ni, Ca, Fe, and O of the 15wt%Ni/85wt%CaFe2O4 catalyst and their oxidation states are fully captured by the XPS.The presence of the elemental components corroborates the EDX and XRD analysis.The atomic concentrations of Ni, Ca, Fe, and O in the catalysts was estimated as 13.4 %, 7.5 %, 20.9 % and 57.8 %, respectively.
The N2 phisorption analysis for the determination of the BET specific surface area and the BJH pore distribution is depicted in Figure 10.The obtained isotherm is typical of a Type-V with H3 hysteresis according to the IUPAC The specific surface area and the pore volume of the catalyst estimated using BET and BJH method are given a 5.13 m 2 /g and 0.01 cm 3 /g, respectively, which is typical of CaFe2O4-containing species [25].
The TPD profile of the 15 wt% Ni/85wt%CaFe2O4 catalyst using NH3 and CO2 as probe gases are depicted in Figure 11 (a) and (b), respectively.It can be seen that distinct desorption peaks at 665 o C and 660 o C was identified for the TPD-NH3 and TPD-CO2 profile, respectively.As a general rule, the desorption of a probe gas at lower temperature range (< 500 o C) signifies weak acid or basic site while desorption at a higher temperature range (> 500 o C) implies strong acid or basic site [26].This implies that the 15wt%Ni/85wt%CaFe2O4 catalyst possesses both strong acid and basic sights which is advantageous for the activation of CH4 and CO2 during methane dry reforming [27].
The spectrum obtained from the analysis of the pure CaFe2O4 support and 15 wt% Ni/85wt%CaFe2O4 catalyst for the nature of chemical bond using FTIR are depicted in Figure 12.Interestingly, the FTIR spectrum revealed a characteristic structure of the CaFe2O4 support.The stretching vibration of OH -signifying adsorbed water molecules can be identified at wavenumber ranged 3500-3000 cm -1 .Similarly, the stretching vibration C-O bond which represents adsorbed atmospheric CO2 can be identified at 1544 -1284 cm -1 .Significantly, metallic bonds were observed at 805 and 692 cm -1 which can be attributed to the stretching vibration of Ca-O and Fe-O metal oxides bond in the CaFe2O3 support [28].Moreover, the catalyst also exhibit stretching

Interaction effect of feed ratio, metal loading and reaction temperature on the CH4 conversion
In the full factorial design of experiments, three factors namely feed ratio, reaction temperature and metal loading were considered.The response and the contour plots showing the effects of feed ratio, reaction temperature and metal loading on the CH4 are depicted in Figure 13.The response plots show the effect of the factors on the catalytic activities in terms of CH4 conversion while the contour plots show the interaction between the factors as they influence the CH4 conversion.Interestingly, the feed ratio, reaction temperature and metal loading show various degrees of influence on the CH4 conversion (cf. Figure 13 (a)).However, the CH4 conversion is mostly influenced by the reaction temperature which is consistent with Arrhenius observation [30].This observation is consistent with the findings of Serrano-Lotina and Daza [31] who reported the influence of reaction temperature ranged 450-850 o C on CH4 conversion.Furthermore, the three factors displayed different level of interactions as shown in Figures 13 (a)-(c).It can be seen that the interaction between the feed ratio and the reaction temperature has more impact on the CH4 conversion at feed ratio ranged 0.7-1.0 and reaction temperature of 800 o C. Similarly, the interaction between the feed ratio and the metal loading show significant influence on the CH4 conversion at metal loading of 10 % and feed ratio ranged 0.7-1.0.The effect of the interaction between the metal loading and the reaction temperature was significant at reaction temperature and metal loading of 800 o C and 10 %, respectively.

Interaction effect of feed ratio, metal loading and reaction temperature on the CO2 conversion
The interaction effects of the reactant feed ratio, metal loading and the dry reforming reaction temperature on CO2 conversion are depicted in Figure 14.The three factors displayed varying level of interaction effect on the CO2 conversion.It can be seen that both the feed ratio and the reaction temperature have signifi-cant effects on the CO2 conversion (Figure 14 (a)).The CO2 conversion increases with feed ratio and reaction temperature.The interaction between the feed ratio and the reaction temperature shows a greater effect on the CO2 conversion at unity feed ratio and reaction temperature of 800 o C as indicated by the red portion of the plot.This trend is in agreement with the findings of Serrano-Lotina and Daza [31] who obtained the highest value of CO2 conversion at reaction temperature and feed ratio of 800 o C and 1, respectively, in methane dry reforming over Ni/Al2O3 catalyst.Contrary to the interaction between the reaction temperature and feed ratio, the interaction between the feed ratio and metal loading did not show pronounce effect on the CO2 conversion.However, based on the interaction plot (Figure 14 (b)) the CO2 conversion was only slightly influenced by the interaction between the feed ratio and metal loading at 1.0 and 10 %, respectively.Moreover, both metal loading and the reaction temperature have increasing effect on the CO2 conversion (Figure 14(c)).It can also been seen that the interaction between the metal loading and the reaction temperature became stronger on the CO2 conversion at metal loading and reaction temperature of 10 % and 800 o C, respectively as indicated by the red portion of the plot.

Interaction effect of feed ratio, metal loading and reaction temperature on the H2 yield
Figure 15 show the interaction effects of feed ratio, metal loading and the reaction temperature on the H2 yield.The three factors vary in level of interaction effects on the H2 yield.There is a significant interaction effect between the feed ratio and the reaction temperature as evident from the increasing trend of the H2 yield (Figure 15 (a)).However, this interaction has greater effect on the H2 yield at unity feed ratio and reaction temperature of 800 o C. The metal loading and feed ratio did not however show good interaction compared to the interaction between feed ratio and reaction temperature.This interaction between the feed ratio and the metal loading shows significant effect on the hydrogen yield at all range of the feed ratio and 10 % metal loading.The interaction between the reaction temperature and metal loading also shows greater effect on the H2 yield at metal loading of 10 % and reaction temperature of 800 o C.

Interaction effect of feed ratio, metal loading and reaction temperature on the CO yield
The interaction effects of the reactant feed ratio, metal loading and reaction temperature on the CO yield are depicted in Figure 16.The three factors have various degrees of interaction effects on the CO yield.The temperature and the feed ratio appear to have higher interaction effect on the CO yield as indicated by red portion of Figures 16 (a).The CO yield increases with the dry reforming reaction temperature while both the feed ratio and the metal loading show less interaction effect on the CO yield.The interaction effect of the reac-  16 (a)-(c) that the feed ratio shows stronger interaction effect at higher temperature and 10% metal loading.

Conclusions
Dry reforming of methane over novel Coand Ni/CaFe2O4 catalysts was carried out for the production of syngas.The catalysts were synthesized using wet-impregnation method and subsequently pre-screened by testing the catalytic performance in methane dry reforming reaction.The pre-screening test showed that the Ni/CaFe2O4 has the best catalytic performance in terms of conversion and yields.Hence, Ni was selected as the active metal to be dispersed on the CaFe2O4 support.Subsequently, full factorial design of experiment was employed to further develop the CaFe2O4 supported Ni catalyst.The interaction effects of factors such as metal loading (5-15%), feed ratios (0.4-1.) and reaction temperature (700-800 o C) were considered on the performance of the Ni/CaFe2O4 in terms of CH4 and CO2 conversion as well as H2 and CO yield.The Ni/CaFe2O4 catalyst showed a promising performance using metal loading of 15 %, reaction temperature of 800 o C and unity feed ratio with highest CH4 and CO2 conversions of 90.04 and 87.67 %, respectively.The 15wt% Ni/CaFe2O4 catalyst was subsequently characterized for its physicochemical properties by TGA, XRD, FE-SEM, EDX, XPS, N2-physisorption, and FTIR.The methane dry reforming over the 15wt% Ni/CaFe2O4 gave syngas ratio of 0.99 making it suitable as a chemical intermediate for the production of oxygenated fuel via Fischer-Tropsch synthesis.
10 ft.1/8 in.OD 2 mm ID, 60/80 mesh, Stainless Steel) and Agilent Hayesep DB (30 ft.1/8 in.OD 2 mm ID, 100/120 mesh, Stainless Steel).Helium (He) gas was used as a carrier with flowrate of 20 mL/min with operating column temperature of 120 o C and detector temperature of 150 o C (column pressure < 90 psi).Separation and quantification of gas analytes viz.

Figure 1 .
Figure 1.Schematic diagram of experimental set-up for the methane dry reforming over the developed catalysts

Figure 2 .
Figure 2. (a) The conversion and yield of CaFe2O4 and the conversions and yields of screened catalysts at (b) 700 o C, (c) 750 o C, (d) 800 o C

Figure 13 .
Figure 13.Response and contour plots for CH4 conversion (a) Effects of feed ratio and reaction temperature (b) Effect of metal loading and feed ratio (c) Effect of metal loading and reaction temperature at atmospheric condition and GHSV of 30000 h -1

Figure 14 .
Figure 14.Response and contour plots for CO2 conversion (a) Effects of feed ratio and reaction temperature (b) Effect of metal loading and feed ratio (c) Effect of metal loading and reaction temperature at atmospheric condition and GHSV of 30000 h -1

Figure 15 .
Figure 15.Response and contour plots for H2 yield (a) Effects of feed ratio and reaction temperature (b) Effect of metal loading and feed ratio (c) Effect of metal loading and reaction temperature at atmospheric condition and GHSV of 30000 h -1

Figure 16 .
Figure 16.Response and contour plots for CO yield (a) Effects of feed ratio and reaction temperature (b) Effect of metal loading and feed ratio (c) Effect of metal loading and reaction temperature at atmospheric condition and GHSV of 30000 h -1 (c)

Table 1 .
Full factorial design of the Ni/CaFe2O4 catalyst