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Efficient and Stable Nanocomposite Catalysts of Ethanol Steam Reforming Prepared via Inexpensive Procedure with Pluronic P123 Copolymer: Characterization and Testing

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19 August 2024

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20 August 2024

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09 December 2024

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Abstract
Mesoporous MgAl2O4+ LnFe0.7Ni0.3O3 (Ln=La, Pr) nanocomposites were prepared by inexpensive one-pot procedure with Pluronic P123 copolymer, Ni+Ru active component was supported by wet impregnation. The real structure of samples was studied by XRD and TEM with EDX, surface properties by FTIRS of adsorbed CO, reactivity by H2 –TPR, catalytic activity was tested in ethanol steam reforming. Disordering of the real structure of nanocomposite supports due to incorporation of transition metal cations into MgAl2O4 results in developed metal-support interface and domination of single surface metal centers. This provides a high catalytic activity in reaction of ethanol steam reforming in the intermediate temperature range ~550 oC close to that of the best known catalysts, and stability to coking. A higher activity for Pr-containing catalyst is provided by a high reactivity of surface oxygen species bound with Pr cations.
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Subject: Chemistry and Materials Science  -   Ceramics and Composites

1. Introduction

Transformation of bio-renewable fuels into syngas and hydrogen is now considered as one of the most important problem of the green energy [1]. Ethanol is among the easy produced, cheap and broadly available fuels, hence, its steam reforming is among the most popular themes of catalysis in this area [2]. In this reaction traditional inexpensive steam reforming catalysts comprised of Ni and/or Co supported on alumina, silica or zeolites suffer from coking leading to fast deactivation [2]. Though Pt group metals possess a higher activity and coking stability [2], a high price makes impossible their practical application. This problem was solved by design of nanocomposite catalysts comprised of mixed oxide supports (with perovskite, fluorite, spinel, etc structures) possessing a high oxygen mobility and reactivity and strongly interacting with loaded nanoparticles of Ni or Ni-based alloys [3]. Coking stability was provided by so called bifunctional mechanism of reforming where fuel molecules are activated on the metal sites, oxidants –on reduced support sites producing reactive oxygen surface species, which rapidly migrate to the metal-support interface and interact with activated fuel fragments producing syngas and preventing their transformation into coke [4]. For realization of this mechanism developed metal-support interface is required. Among attractive approaches to provide such interface, ex-solution of metal nanoparticles (Ni, Co, etc.) from the complex oxides with perovskite, spinel, fluorite, etc structures under reducing conditions is to be mentioned [5,6,7]. In this case both epitaxy of metal clusters with the surface of support as well as their decoration by oxidic fragments provide developed interface, which helps also to prevent sintering of Ni in reaction conditions. While for fluorite-like complex oxides PrSmCeZrO2 doped with Ni specific surface area remains sufficiently high, for perovskite-like oxides containing in B positions Mn, Fe, Cr etc. cations, along with Ni and Ru, specific surface area after calcinations in the range of 700-900 oC is ~ 4-7 m2/g [8], which is not good for the practical application. Preparation of nanocomposites comprised of perovskite (P) and fluorite (F) allowed to stabilize the surface area of catalysis after Ni segregation, apparently due to hampering migration of cations between perovskite nanodomains due to presence of fluorite nanodomains as barriers [9]. While one-pot Pechini route of P+F nanocomposite synthesis has not allowed to obtain nanodomains of perovskite phase due to incorporation of transition metal cations into fluorite domains, it was possible to prepare nanocomposite containing perovskite nanodomains when fluorite nanopowders were dispersed in the perovskite polymeric precursor solution with subsequent evaporation and calcination [9]. Another approach to stabilize dispersion of perovskite-based active component with Ni is to load it by simple wet impregnation on mesoporous MgAl2O4 support prepared by one-pot evaporation-induced self-assembly method, though incorporation of transition metal cations into the spinel lattice takes place, and diffraction peaks of the perovskite phase were not observed even for supported 20 wt.% PrNi0.9Ru0.1O3 due to small size and disordering of perovskite domains [10]. Along with reactive surface oxygen species provided by supported perovskite layers, presence of Mg in this spinel support also helps to suppress coking due to decreasing density of acid sites responsible for ethylene formation and coke generation [2,4,10,11]. To simplify further preparation procedure, it seems interesting to try one-pot synthesis, when in preparation of mesoporous materials with the help of Pluronic P123 copolymer [10] all cations of perovskite can be mixed with Mg and Al cations in one solution, and then typical procedure of mesoporous materials synthesis will be applied. No doubts that a part of transition metal cations will be incorporated into MgAl2O4 lattice. Since doping of MgAl2O4 by Fe, Cr and Ti cations was already demonstrated to be a good option for increase of supported nanocomposites activity and stability in fuels reforming into syngas [11], testing this promising procedure in synthesis of nanocomposites comprised of perovskites LaFe0.7Ni0.3O3 or PrFe0.7Ni0.3O3 with MgAl2O4 is worth trying, which is the purpose of this paper.

2. Materials and Methods

2.1. Catalysts Preparation

Next reagents were used for synthesis: P123 Pluronic triblock copolymer ((EO)20(PO)70(EO)20 (Mn=5800, Sigma Aldrich), aluminum isopropoxide (Al(OPri)3), (Acros Organics), HNO3 (REACHIM), Ni(NO3)2*6H2O (Acros Organics), Mg(NO3)2*6H2O (REACHIM), Pr(NO3)3*nH2O(Vecton). Synthesis procedure is further described in details on example of the first nanocomposite. First solution was prepared by adding 60 ml EtOH to 6.0 g of Pluronic P123 and stirring by a magnetic stirrer for 1 hour. Second solution was prepared by adding 30 ml EtOH and 2 ml of HNO3 to 8.61g of aluminum isopropoxide and stirring for 1 h. Then two solutions were mixed and after stirring for 0.5 h 5.37g. of Mg(NO3)2*6H2O were added. After stirring for 0.5 h 2.96 g of Fe nitrate and 0.72 g of Pr(NO3)3*nH2O were added and stirred for 3 h., then solution was dried at 60 ° for 72 h. A dried polymeric mixture was placed into a tubular reactor and heated in the stream of air with the heating rate of 1o per minute to 700 oC and kept at this temperature for 5 h. 5%Ni +1%Ru were supported by impregnation method using mixed solutions of Ni(NO3)2*nH2O (Vecton) and crystalline anhydrous RuOCl3 (REACHIM) followed by drying and calcination at 700 oC for 1 h.

2.2. Catalysts Characterization

Diffraction patterns were got using a Bruker Advance D8 diffractometer with CuKα radiation (γ 1.5418 Å). Scanning was performed in the range of angles 15-90 (2θ) degrees with a scanning step of 0.05 (2θ) and accumulation time 3 s. The diffractograms were processed using the EVA program included in the diffractometer software package identification of the obtained phases.
High resolution transmission electron microscopy (HRTEM) images were obtained with a JEM-2200FS transmission electron microscope (JEOL Ltd., Japan, acceleration voltage 200 kV, lattice resolution 1Å) equipped with a Cs-corrector and EDX spectrometer (JEOL Ltd., Japan). The samples for the TEM study were prepared by ultrasonic dispersion in ethanol and consequent deposition of the suspension upon a "holey" carbon film supported on a copper grid. The minimum spot diameter for the step-by-step line or mapping elemental EDX analysis was ∼1 nm with a step of about 1.5 nm.
The specific surface area of samples was evaluated by the Brunnauer–Emmet–Teller (BET) method by recording nitrogen physical adsorption at the liquid nitrogen temperature using an ASAP-2400 (Micromeritics Instrument. Corp., Norcross, GA, USA) automated volumetric adsorption unit. Before the analysis, samples were outgassed at 150°C for 4 h at a pressure of 1 × 10–3 Torr (∼0.1 Pa). The obtained adsorption isotherms were used to calculate the specific surface area and pore size distribution.
The surface properties of samples were studied using low-temperature Fourier –transformed infrared spectroscopy of adsorbed carbon monoxide (FTIRS of adsorbed CO). Samples were pressed into pellets with sizes of 1х2 cm2 and weight of 40 mg, then put into the IR cell and heated in vacuum to 500 °C followed by H2 addition to 200 Torr and reducing for 1 h at this temperature. Then cell was evacuated up to a residual pressure below 10-4 Torr and cooled to a room temperature. Spectra were registered on a Shimadzu IRTracer-100 spectrometer in the range of 400-6000 cm-1 with a resolution of 4 cm-1 and 200 scans accumulation. CO was adsorbed at -196 oC and CO pressure from 0.1 to 10 Torr. After spectra recording at -196 oC the cell was heated to a room temperature and spectra were registered. These spectra recorded in the absorption scale were normalized on the optical thickness of a pellet and a spectrum before CO adsorption was subtracted from that after CO adsorption. Spectra analysis was carried out by deconvolution of corresponding IR bands on individual Gaussian components. Concentrations of different adsorption centers were estimated from the integral intensities of observed characteristic absorption bands using integral absorption coefficients [12].
Material reactivity was characterized by the temperature-programmed reduction by H2 (TPR-H2) (10% H2 in Ar, the feed rate 2.5 L/h and the temperature ramp from 25 to 900°C at 10°C/min) in a flow kinetic setup with a quartz U-shaped reactor equipped with a Tsvet-500 chromatograph and a thermal conductivity detector.
Ethanol steam reforming (ESR) was conducted in a continuous flow fixed-bed quartz reactor under atmospheric pressure in the temperature range of 550-700 °C. A total of 30 mg of catalyst (0.25-0.5 mm fraction) was loaded and sandwiched between two quartz wool layers. Prior to the activity test, the catalyst was reduced with 5 vol% H2/Ar (100 mL/min) at 650 °C for 1 h. EtOH and H2O mixture was heated to 120 °C and mixed with N2 stream coming from the mass-flow controller, yielding a typical feed gas composition of EtOH/H2O = ¼, C(EtOH) = 2% vol. The outlet products were analyzed by gas chromatography using a Tsvet-500 chromatograph. To ensure fast steady-state achievement, experiments were started at 700 °C keeping for one hour at this temperature, then decreasing it by the step of 50 °C to 550 °C keeping for one hour at each temperature as well.

3. Results

3.1. Structural and Textural Properties

Figure 1 and Figure 2 present diffraction patterns of studied samples. In both La-containing samples MgAl2O4 spinel phase [PDF 00-021-1152] with crystallite sizes 200 Å and the lattice parameter 8.08 Å was identified. Two perovskite phases corresponding to LaFe0.75Ni0.25O3 [PDF 01-088-0639] and LaNiO3 [PDF 00-033-0710] were observed. In both patterns broad diffraction peaks are also present corresponding to the cubic Fm-3m structure of Mg(Ni)O with parameters 4.213 Å and 4.182 Å for support and catalyst respectively. Moreover, in support La10Al4O21 phase [PDF 00-039-0009] was observed which is absent after supporting Ni and Ru oxides due to interaction with impregnating solution. Diffraction patterns of Pr-containing samples (Figure 2) are characterized by broader diffraction peaks compared with La-containing samples (Figure 1), indicating a higher disordering. It is reflected in smaller (90-120 Å) sizes of MgAl2O4 spinel phase domains, while diffraction peaks corresponding to perovskite phase are very weak or absent. This correlates with presence of strong PrO2 diffraction peaks with domains sizes ~90 -110 Å, thus indicating instability of perovskite PrFe0.75Ni0.25O3 phase in combination with MgAl2O4 spinel phase due to incorporation of transition metal cations into spinel lattice [11]. After loading NiO+RuO2 the intensity of PrO2 peaks decreases, apparently due to formation of disordered praseodimium nickelates fragments, while appearance of RuO2 peaks indicates that Ru is in part deposited as RuO2 nanoparticles. Similar to the case of samples with La, in Pr-containing samples Mg(Ni)O solid solution phase is present as well.
TEM images of catalysts samples are presented in Figure 3 and Figure 4. For both types of catalysts the particles are composed of stacked nanodomains of different orientation and disordering degree apparently corresponding to different phases in agreement with XRD data.
EDX data (Table 1) for 5%Ni+1%Ru/(50%MgAl2O4+ 50%LaFe0.75Ni0.25O3) catalyst demonstrate rather moderate spatial variation of Ni concentration in the surface layer of nanocomposite, which is good for ensuring reproducibility of catalytic properties. Note that for nanocomposite LaMn0.45Ni0.45Ru0.1O3 + Pr0.15Sm0.15Ce0.35Zr0.35O2 prepared by one-pot Pechini route [9] strong spatial variation of Ni content, and, hence, degree of Ni agglomeration and interaction with support resulted in a low catalytic activity. A high content of Ru revealed in Figure 4d is apparently due to presence of RuO2 particle as agrees with XRD data (Figure 1). A high content of Mg in all places also agrees with presence of NiO-MgO phase revealed by XRD, which provides strong Ni-support interaction required for coking suppression. Since according to XRD data (vide supra) for 50%MgAl2O4 + 50%PrFe0.7Ni0.3O3 nanocomposite perovskite phase was absent due to strong incorporation of Ni and Fe cations into the spinel lattice, and specific surface area is higher (vide infra), while Mg(Ni)O solid solution phase is present in the catalyst, even more uniform distribution of Ni on this catalyst surface is expected.
Table 2 presents data on specific surface area (SSA) of catalysts samples. They are reasonably high though being lower than those for catalysts based on doped MgAl2O4 with supported active components, where values ~ 100 m2/g were obtained [11]. Hence, as expected, transition metal and rare earth cations apparently helps sintering of spinel nanodomains. However, SSA values are better than those for catalysts based on perovskite-fluorite nanocomposites with specific surface areas ~20 m2/g [9]. A higher specific surface area for Pr-containing sample can be explained by a small content of the PrFe0.7Ni0.3O3 perovskite phase, since perovskite phases are known by their strong sinterability [8].

3.2. Surface Properties

Identification of the surface sites and characterization of their properties were carried out by FTIRS using CO as a test molecule. Figure 5 presents spectra of CO adsorbed on 50%MgAl2O4+50%LaFeNiO3 (co- synthesis sample) at -196 oC with pressure variation from 0.1 to 10 Torr. Bands at 2148 and 2160 cm-1 correspond to CO adsorption on different cations and OH-groups, while the band at 2139 cm-1 can be assigned to physically adsorbed СО [13,14]. Low intensity bands at 2065 and 2080 cm-1 correspond to СО complexes with metal sites, apparently, Ni0 [15,17]. Band at 2080 cm-1 with CO pressure increase shifts to 2090 cm-1. After heating sample to room temperature the bands of adsorbed CO were not revealed.
Figure 6 presents spectra of CO adsorbed on (5%Ni+1%Ru)/MgAl2O4+LaFeNi (co- synthesis) sample at -196 oC and 0.1-10 Torr CO pressure. Bands at 2158 и 2170 cm-1 characterize CO adsorption on the support centers, while the bands at 1945, 2045 и 2080 cm-1 correspond to СО adsorbed on metal sites [13,14,15]. Bands at 2045 и 2080 cm-1 are due to terminal CO complexes, while the band at 1945 cm-1 refers to bridging carbonyls [16,17]. As expected, intensity of bands corresponding to CO adsorbed on metal sites for catalyst with supported Ru+Ni is much higher than that for initial 50%MgAl2O4+50%LaFeNiO nanocomposite.
After sample heating from liquid nitrogen temperature to the room temperature a broad band with a maximum at 2065 cm-1 remained in spectrum (Figure 7).
Deconvolution of this band into Gaussian components revealed 4 bands with maxima at 1965, 2020, 2050 and 2073 cm-1. The first band corresponds to bridging form of CO adsorption on metal sites, while the other three refer to terminal complexes. Estimated concentration of metal sites is equal to 6 and 11 μmol/g for bridging and terminal carbonyls, respectively.
Figure 8 presents FTIR spectra of CO adsorbed on Ni+Ru/MgAl2O4+PrFeNiO3 sample at -196 oC with pressure variation from 0.1 to 10 Torr.
Bands at 2158, 2165 and 2215 cm-1 characterize СО adsorption on support sites [13,14], while the bands at 2040 and 2080 сm-1 correspond to СО adsorbed on metal sites as terminal carbonyls [15,16,17]. Band at 2080 сm-1 with the increase in СО pressure shifts to 2090 cm-1, which is typical for СО adsorbed in linear configuration on metal planes.
When the sample was heated from the liquid nitrogen temperature to the room temperature (Figure 9), the band with maximum at 2058 cm–1 remained in the FTIR spectrum. Deconvolution of this band into Gaussian components revealed the bands with maxima at 1995, 2043, 2058, and 2080 cm–1. The first band corresponds to bridging forms of CO adsorption on metal particles, while other three- to terminal ones [15,16,17,18]. Estimated concentration of surface sites is equal to 3 and 11 μmole /g for bridging and terminal carbonyls, respectively. A higher share of terminal carbonyls for Pr-containing catalysts apparently correlates with a higher specific area as well as with a higher nanocomposite support disordering, which helps to provide a higher Ni and Ru dispersion and a higher degree of metal-support interaction leading to decoration of the surface of Ni/Ru nanoparticles/clusters by oxidic fragments. Note that for both catalysts, the density of isolated metal sites stabilizing terminal carbonyls (11 μmole /g) is quite close to that for catalysts NiRu/PrCeZrO/MgAl1.9Me0.1O4 (Me=Ti, Fe, Cr) (in the range of 9.5-14 μmole /g) with higher specific surface areas (85-110 m2/g) at the same amount of supported metals 5%Ni+1%Ru [11]. Hence, disordering of the surface layers of nanocomposite supports indeed helps to provide high dispersion of supported metals.

3.3. H2 TPR

H2-TPR curves for both catalysts (Figure 10 and Figure 11) contain two narrow peaks in the range of 200-300 oC corresponding to reduction of RuO2 and NiO nanoparticles and their mixed clusters conjugated with reduction of Pr and Fe cations in the surface layer [9,10,11].
A higher intensity of the peak at ~ 250 oC for Pr-containing catalyst is explained by a smaller content of pure RuO2 particles due to a stronger interaction between Pr and Ni oxidic species forming surface nanoparticles of Pr nickelates including Ru cations as well (vide supra). Broad peaks in the range of 400-900 oC are related to reduction of both perovskite phases, NiMgO phase as well as Fe and Ni cations incorporated into the bulk of MgAl2O4 particles [9,10,11]. A lower intensity of this peak for Pr-containing catalyst apparently correlates with absence of the bulk PrFe0.75Ni0.25O3 phase in support.

3.4. Catalytic Activity

Figure 12 and Figure 13 present temperature dependencies of ethanol steam reforming products concentrations. At each temperature performance was stable not suffering from any decline, which is explained by coking and sintering stability typical for nanocomposite active components based on mesoporous MgAl2O4. Hence, one-pot synthesis route of nanocomposites used in this work has not deteriorated such important advantage of these catalyst. At 550 oC concentration of hydrogen is higher for Pr-containing catalyst, which correlates with a higher share of CO2 in products. This can be explained by a higher activity of this catalyst in the water gas shift reaction due to positive effect of Pr cations, which helps also to provide a higher activity in ethanol reforming (a higher total concentration of products CO+CO2 +CH4) despite identical density of isolated active metal sites stabilizing terminal carbonyls (vide supra). Though for this catalyst hydrogen content increases with temperature correlating with decrease of methane byproduct content (Figure 12), at 700 oC it is slightly less than for La-containing catalyst (~7% versus ~8.6%). This apparently correlates with the decrease of CO2 content with temperature due to effect of reverse water gas shift reaction, while for La-containing catalyst CO2 concentration is nearly constant due to less efficiency in this reaction.
At 550 oC when ethanol conversion is usually in the range of 50-85%, in Table 3 comparison of hydrogen yield (Y(H2) =[C(H2)/6 C0(EtOH)]x100) is given for nanocomposite catalysts prepared in this work as well as for those prepared by supporting 5%Ni+1%Ru/Pr0.3Ce0.35Zr0.35O2 on doped MgAl2O4 spinel [11] or supporting Ni on perovskite + fluorite nanocomposites prepared by one-pot Pechini route, by dispersion of the mixture of perovskite and fluorite nanoparticles in solution of polyvinyl butyral in isopropanol followed by drying and calcination; or sequential route based on dispersion of fluorite nanoparticles in polymeric Pechini precursor of perovskite phase followed by required thermal treatment [9,19]. Hydrogen yield is comparable for majority of catalysts demonstrating that for catalysts prepared in this work using simplified one-pot procedure to make nanocomposite support their efficiency is fine. At the same time for catalyst based on perovskite+ fluorite support prepared by one-pot Pechini route efficiency is the lowest correlating with the absence of perovskite phase in this case [19]. At the same time one-pot procedure of nanocomposite preparation using P123 Pluronic triblock copolymer ensured a high surface area and good activity of 5%Ni+1%Ru/(MgAl2O4+ PrFe0.7Ni0.3O3) catalyst despite absence of reflections corresponding to PrFe0.7Ni0.3O3 phase. It is explained by formation of disordered Pr nickelate fragments strongly interacting with Fe-modified spinel support. Interaction of Pr cations with metal alloy nanoparticles as well as their presence in the oxide support surface layer provide both higher efficiency of ethanol activation as well as a higher concentration of reactive oxygen species on support [3,8], which ensure a higher activity of Pr-containing catalyst compared with that containing La.

4. Discussion

Hence, a simple and inexpensive one-pot procedure of nanocomposite MgAl2O4+ LnFe0.7Ni0.3O3 preparation with subsequent supporting Ni+Ru by co-impregnation allowed to obtain efficient and stable to coking catalysts of ethanol steam reforming, which is provided by optimized interaction between spinel and perovskite phases ensuring also strong interaction of metal alloy nanoparticles with these supports and their high dispersion. Though these catalysts were tested here only in diluted feed, for mesoporous catalysts based on MgAl2O4 support our previous studies demonstrated that a high and stable performance in this reaction in diluted feed reliably correlates with a high activity and coking/sintering stability in concentrated feeds in other reactions such as methane steam/dry reforming and biofuels steam/ autothermal reforming [10,11]. This apparently opens good prospects of this preparation procedure for design of mesoporous nanocomposite active components for structured catalysts of fuels transformation into syngas. Clearly, optimization of the nanocomposite support chemical composition by varying the nature and content of transition and rare earth cations will further improve these catalysts perforance. Moreover, since comparison of performance in reactions of methane dry reforming and ethanol steam reforming of our catalysts based on doped MgAl2O4 support with that of catalysts on other supports presented in a lot of published papers demonstrated their much higher specific catalytic activity [11], there is clearly a good chance of their broad practical application, with a due regard for their inexpensive composition and preparation procedure.

5. Conclusions

Inexpensive one-pot procedure of mesoporous nanocomposite MgAl2O4+ LnFe0.7Ni0.3O3 (Ln=La, Pr) synthesis with Pluronic P123 copolymer was applied for the first time. Disordered structure of obtained nanocomposites was formed due to incorporation of transition metal cations into spinel structure. This provides strong interaction of loaded by wet co-impregnation Ni+Ru active component with these nanocomposite supports leading to its uniform spatial distribution and decoration of metal alloy nanoparticles in reduced catalysts by oxidic fragments. It leads to developed metal-support interface and domination of single surface metal centers as demonstrated by such unique and reliable method as FTIRS of adsorbed CO. In reaction of ethanol steam reforming this results in a high catalytic activity close to that of best catalysts based on MgAl2O4 and stability to coking. A higher yield of hydrogen at 550 oC for Pr-containing catalyst is provided by a higher reactivity of surface oxygen species bound with Pr cations.

Author Contributions

Conceptualization, V.S. and B.M.; investigation, N.T., J.F., N.G., T.K.,V.R., A.I.; writing—original draft preparation, N.T., T.G., T.K.; writing—review and editing, V.S.; supervision, V.S. and B.M. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Russian Federation Ministry of Science and Higher Education through the state research target for the Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences (project FWUR-2024-0033). The authors acknowledge the Shared Research Center “VTAN” of the Novosibirsk State University supported by Ministry of Science and Higher Education of the Russian Federation by agreement #075-12-2021-697 for TEM investigations.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. XRD patterns of nanocomposite support 50%MgAl2O4+50%LaFe0.75Ni0.25O3 (1) and (5%Ni+1%Ru)/(50%MgAl2O4+50%LaFe0.75Ni0.25O3) catalyst (2). Sp – MgAl2O4 [PDF 00-021-1152], * - LaFe0.75Ni0.25O3 [PDF 01-088-0630], + - LaNiO3 [PDF 00-033-0710], ^ - MgO-NiO [PDF 01-078-0430 MgO], | - RuO2 [PDF 03-065-2824], ~ - La10Al4O21 [PDF 00-039-0009]. Moreover, positions of some phases diffraction peaks are marked by lines.
Figure 1. XRD patterns of nanocomposite support 50%MgAl2O4+50%LaFe0.75Ni0.25O3 (1) and (5%Ni+1%Ru)/(50%MgAl2O4+50%LaFe0.75Ni0.25O3) catalyst (2). Sp – MgAl2O4 [PDF 00-021-1152], * - LaFe0.75Ni0.25O3 [PDF 01-088-0630], + - LaNiO3 [PDF 00-033-0710], ^ - MgO-NiO [PDF 01-078-0430 MgO], | - RuO2 [PDF 03-065-2824], ~ - La10Al4O21 [PDF 00-039-0009]. Moreover, positions of some phases diffraction peaks are marked by lines.
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Figure 2. XRD patterns of nanocomposite support 50% MgAl2O4+50% PrFe0.75Ni0.25O3 (1) and (5%Ni+1%Ru)/(50%MgAl2O4+50%PrFe0.75Ni0.25O3) catalyst (2). Sp – MgAl2O4 [PDF 00-021-1152], * - perovskite [PDF 01-074-1472], + - PrO2 [PDF 00-006-0329], ^,^ - MgO-NiO [PDF 01-078-0430 MgO], | - RuO2 [PDF 03-065-2824]. Moreover, positions of some phases diffraction peaks are marked by lines.
Figure 2. XRD patterns of nanocomposite support 50% MgAl2O4+50% PrFe0.75Ni0.25O3 (1) and (5%Ni+1%Ru)/(50%MgAl2O4+50%PrFe0.75Ni0.25O3) catalyst (2). Sp – MgAl2O4 [PDF 00-021-1152], * - perovskite [PDF 01-074-1472], + - PrO2 [PDF 00-006-0329], ^,^ - MgO-NiO [PDF 01-078-0430 MgO], | - RuO2 [PDF 03-065-2824]. Moreover, positions of some phases diffraction peaks are marked by lines.
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Figure 3. TEM images of (5%Ni+1%Ru)/(50%MgAl2O4+50%PrFe0.75Ni0.25O3) catalyst.
Figure 3. TEM images of (5%Ni+1%Ru)/(50%MgAl2O4+50%PrFe0.75Ni0.25O3) catalyst.
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Figure 4. TEM images of (5%Ni+1%Ru)/(50%MgAl2O4+50%LaFe0.75Ni0.25O3) catalyst.
Figure 4. TEM images of (5%Ni+1%Ru)/(50%MgAl2O4+50%LaFe0.75Ni0.25O3) catalyst.
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Preprints 115645 g005
Figure 5. Spectra of CO adsorbed on 50%MgAl2O4+50% LaFe0.7Ni0.3O3 nanocomposite at -196 oC and 0.1-10 Torr pressure.
Figure 5. Spectra of CO adsorbed on 50%MgAl2O4+50% LaFe0.7Ni0.3O3 nanocomposite at -196 oC and 0.1-10 Torr pressure.
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Figure 6. Spectra of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+ 50% LaFe0.7Ni0.3O3) catalyst at -196 oC and 0.1-10 Torr pressure.
Figure 6. Spectra of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+ 50% LaFe0.7Ni0.3O3) catalyst at -196 oC and 0.1-10 Torr pressure.
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Figure 7. FTIR spectrum of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+ 50% LaFe0.7Ni0.3O3) sample at room temperature and 10 Torr CO pressure, the decomposition into Gaussian components is shown.
Figure 7. FTIR spectrum of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+ 50% LaFe0.7Ni0.3O3) sample at room temperature and 10 Torr CO pressure, the decomposition into Gaussian components is shown.
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Figure 8. FTIR spectra of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+50% PrFe0.7Ni0.3O3 ) catalyst at -196 oC and 0.1-10 Torr pressure.
Figure 8. FTIR spectra of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+50% PrFe0.7Ni0.3O3 ) catalyst at -196 oC and 0.1-10 Torr pressure.
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Figure 9. FTIR spectra of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+50% PrFe0.7Ni0.3O3) catalyst at room temperature and 10 Torr CO pressure.
Figure 9. FTIR spectra of CO adsorbed on (5%Ni+1%Ru)/(50%MgAl2O4+50% PrFe0.7Ni0.3O3) catalyst at room temperature and 10 Torr CO pressure.
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Figure 10. H2 TPR for (5%Ni+1%Ru)/(50%MgAl2O4+ 50% LaFe0.7Ni0.3O3 ) catalyst.
Figure 10. H2 TPR for (5%Ni+1%Ru)/(50%MgAl2O4+ 50% LaFe0.7Ni0.3O3 ) catalyst.
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Preprints 115645 g011
Figure 11. H2 TPR for (5%Ni+1%Ru)/(50%MgAl2O4+ 50% PrFe0.7Ni0.3O3) catalyst.
Figure 11. H2 TPR for (5%Ni+1%Ru)/(50%MgAl2O4+ 50% PrFe0.7Ni0.3O3) catalyst.
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Figure 12. Temperature dependences of reaction products concentrations in the process of ethanol steam reforming on (5%Ni+1%Ru)/(MgAl2O4+PrFe0.7Ni0.3O3) catalyst. Feed 2%EtOH+ 8%H2O+N2, contact time 10 ms.
Figure 12. Temperature dependences of reaction products concentrations in the process of ethanol steam reforming on (5%Ni+1%Ru)/(MgAl2O4+PrFe0.7Ni0.3O3) catalyst. Feed 2%EtOH+ 8%H2O+N2, contact time 10 ms.
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Preprints 115645 g013
Figure 13. Temperature dependences of reaction products concentrations in the process of ethanol steam reforming on (5%Ni+1%Ru)/(MgAl2O4+ LaFe0.7Ni0.3O3) catalyst. Feed 2%EtOH+8%H2O+N2, contact time 10 ms.
Figure 13. Temperature dependences of reaction products concentrations in the process of ethanol steam reforming on (5%Ni+1%Ru)/(MgAl2O4+ LaFe0.7Ni0.3O3) catalyst. Feed 2%EtOH+8%H2O+N2, contact time 10 ms.
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Table 1. EDX data on the elemental composition of 5%Ni+1%Ru/(50%MgAl2O4+ 50%LaFe0.75Ni0.25O3) catalyst particles in regions a–d in Figure 4.
Table 1. EDX data on the elemental composition of 5%Ni+1%Ru/(50%MgAl2O4+ 50%LaFe0.75Ni0.25O3) catalyst particles in regions a–d in Figure 4.
Region
in Figure 4 		Concentration of elements by EDX, at. %
Ni Ru La Fe Mg Al
a 16.1 0.7 17.1 11.0 16.9 38.2
b 16.9 0.8 27.4 15.4 22.9 16.6
c 10.5 0.4 13.7 6.9 20.5 47.9
d 15.9 15.5 23.3 15.6 11.9 17.8
Table 2. Textural characteristics of samples.
Table 2. Textural characteristics of samples.
Sample SSA, m2/g Vpores, cm3/g Dav., nm
(5%Ni+1%Ru)/(50%MgAL2O4+ 50%LaFe0.7Ni0.3O3 ) 42 0.13 120
(5%Ni+1%Ru)/(50%MgAl2O4 + 50%PrFe0.7Ni0.3O3 ) 83 0.07 140
Table 3. Comparison of H2 yield in the reaction of ethanol steam reforming at 550 oC on nanocomposite catalysts. Feed 2%EtOH+8%H2O+N2, contact time 10 ms.
Table 3. Comparison of H2 yield in the reaction of ethanol steam reforming at 550 oC on nanocomposite catalysts. Feed 2%EtOH+8%H2O+N2, contact time 10 ms.
Catalyst H2 yield, % Reference
5%Ni+1%Ru/(MgAl2O4+ LaFe0.7Ni0.3O3) 38 This work
5%Ni+1%Ru/(MgAl2O4+PrFe0.7Ni0.3O3) 46 This work
5%Ni+1%Ru/Pr0.3Ce0.35Zr0.35O2/MgAl1.9Fe0.1O4 51 [11]
5%Ni+1%Ru/Pr0.3Ce0.35Zr0.35O2/MgAl1.9Ti0.1O4 45 [11]
5%Ni+1%Ru/Pr0.3Ce0.35Zr0.35O2/MgAl1.9Cr0.1O4 47 [11]
5%Ni/[Pr0.15Sm0.15Ce0.35Zr0.35O2+ LaMn0.9Ru0.1O3] one-pot 18 [19]
5%Ni/[Pr0.15Sm0.15Ce0.35Zr0.35O2+LaMn0.9Ru0.1O3] dispersion 45 [19]
5%Ni/[Pr0.15Sm0.15Ce0.35Zr0.35O2+ LaMn0.9Ru0.1O3] sequential 47 [19]
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