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Article

Supported Nanostructured MoxC Materials for the Catalytic Reduction of CO2 through the Reverse Water Gas Shift Reaction

by
Arturo Pajares
1,2,†,
Xianyun Liu
1,‡,
Joan R. Busacker
1,
Pilar Ramírez de la Piscina
1 and
Narcís Homs
1,2,*
1
Departament de Química Inorgànica i Orgànica, Secció de Química Inorgànica & Institut de Nanociència i Nanotecnologia (IN2UB), Universitat de Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain
2
Catalonia Institute for Energy Research (IREC), Jardins de les Dones de Negre 1, 08930 Barcelona, Spain
*
Author to whom correspondence should be addressed.
†
Present address: Sustainable Materials Management, Flemish Institute for Technological Research (VITO NV), Boeretang 200, 2400 Mol, Belgium.
‡
Present address: College of Chemistry and Chemical Engineering, Henan Polytechnic University, Jiaozuo 454003, China.
Nanomaterials 2022, 12(18), 3165; https://doi.org/10.3390/nano12183165
Submission received: 27 July 2022 / Revised: 5 September 2022 / Accepted: 9 September 2022 / Published: 13 September 2022
(This article belongs to the Special Issue State-of-the-Art Nanomaterials for Energy Storage/Conversion and Catalysis in Spain)
Browse Figures
Versions Notes

Abstract

:
MoxC-based catalysts supported on γ-Al2O3, SiO2 and TiO2 were prepared, characterized and studied in the reverse water gas shift (RWGS) at 548–673 K and atmospheric pressure, using CO2:H2 = 1:1 and CO2:H2 = 1:3 mol/mol reactant mixtures. The support used determined the crystalline MoxC phases obtained and the behavior of the supported nanostructured MoxC catalysts in the RWGS. All catalysts were active in the RWGS reaction under the experimental conditions used; CO productivity per mol of Mo was always higher than that of unsupported Mo2C prepared using a similar method in the absence of support. The CO selectivity at 673 K was above 94% for all the supported catalysts, and near 99% for the SiO2-supported. The MoxC/SiO2 catalyst, which contains a mixture of hexagonal Mo2C and cubic MoC phases, exhibited the best performance for CO production.

Graphical Abstract

1. Introduction

In addition to capture and storage of CO2, nowadays there is a clear interest in its use as an out-stream chemical feedstock in order to actively contribute to the reduction of CO2 emissions; CO2 can be considered a cheap carbon C1 source for upgrading rather than a waste with consequences in global warming [1,2,3,4]. However, the direct transformation of CO2 to useful products is difficult. The high chemical stability of CO2 difficult its catalytic transformation, the developing of new materials capable of efficiently bind and activate this molecule is nowadays an active research area. An interesting CO2 utilization approach is its reduction to CO, employing H2 as a reducing agent via the reverse water gas shift (RWGS) reaction [5,6,7,8]:
CO2 + H2 → CO + H2O
The reduction of CO2 to CO with renewable H2 can be regarded as a simple and easy path for CO2 recycling, which would allow its reuse at a large scale. After the RWGS step and H2O separation, a CO2/CO/H2 out-stream mixture can be produced. This out-stream can be used as syngas input for other well-established chemical processes, such as Fischer-Tropsch (FT) or methanol synthesis [9,10,11,12,13,14,15].
The RWGS reaction can be carried out using noble metal-based catalysts [5,10,16]. Due to the similar properties of transition metal carbides (TMCs) and Pt-based catalysts, the formers have been proposed as catalysts for different processes in which Pt-based catalysts are active [17,18]. One of these processes is the CO2 reduction to CO, which has been analyzed over different TMCs using theoretical and experimental approaches [19,20,21,22,23,24,25].
The preparation of TMCs is usually carried out using carburization methods. These methods apply high temperature and/or pressure conditions in the presence of a reducing atmosphere, usually mixtures of H2 and carbon-containing gases (CO, CH4, C2H4) [25,26,27,28]. Due to the increased interest in TMC-based catalysts, in recent years, greener preparation methods have been explored [21,22,29,30,31]. In an earlier investigation, we studied the preparation of bulk MoxC catalysts using different molybdenum and carbon precursors and following sol-gel based routes; the bulk MoxC catalysts generated, contained different crystalline phases, which influenced their catalytic behavior in the RWGS reaction [31].
The deposition onto a support of the appropriate TMC active phase can be an interesting approach to improve the catalytic behavior of bulk TMCs materials, which usually show low surface area values. Supported MoxC phases have been used as catalysts in different processes such as CH4 dry reforming [32], hydrazine decomposition [33], thiophene hydrodesulfurization [34], propene and tetralin hydrogenation [35] and Fischer-Tropsch synthesis [36]. However, supported MoxC catalysts have not been much studied in the RWGS reaction [37,38,39]. Porosoff et al. have reported the promoter effect of K in Al2O3- supported Mo2C-based catalysts containing MoO2 and/or metallic Mo, which were prepared by carburization with CH4/H2 at 873 K [38]. Sub-nanosized molybdenum carbide clusters highly dispersed onto N-doped carbon/Al2O3, prepared by carbonization of MoO3 with glucose, were more performant in the RWGS than bulk β-Mo2C [39]. Recently, the preparation of SiO2- and SBA-15-supported Mo2C-based catalysts (20% wt Mo), using different routes of Mo incorporation to the support and a final carburization process with CH4/H2, has been studied [40]. The preparation method and the support influenced the composition of MoxCy crystalline phases developed and therefore the catalytic performance of the material in the RWGS [40]. The preparation of MoxC-based catalysts supported onto γ-Al2O3, SiO2 and MFI-type zeolites by incipient wetness impregnation of ammonium molybdate and carburization with CH4/H2, have led to catalysts with different Mo-containing species such as Mo2C, MoO3 and Mo0; the phases developed and the catalytic performance in the RWGS of the materials depended also on the support characteristics [41].
Here, MoxC phases were generated onto γ-Al2O3, SiO2 and TiO2 by a thermal treatment of the solid obtained from the interaction between a MoCl5/urea solution and the corresponding oxide. The crystalline MoxC phases obtained depended on the support used in the preparation and determined the catalytic behavior of materials in the RWGS.

2. Experimental

2.1. Preparation of Catalysts

Commercial γ-Al2O3 (Alfa Aesar, Haverhill, MA, US, 226 m2 g−1), SiO2 (Degussa, Frankfurt, Germany, 200 m2 g−1) and TiO2 (Tecnan, Navarra, Spain, 117 m2 g−1, anatase/rutile, 78/22% wt) were employed as supports. Urea (Alfa Aesar, Haverhill, MA, US, 99%), which was used as carbon source, was added to a solution of MoCl5 (Alfa Aesar, Haverhill, MA, US, 99.6%) in ethanol with a urea/MoCl5 = 7 molar ratio [21,29,31]. The viscous solution was contacted with the respective powdered support. The resulting solid was dried at 333 K, and then treated under Ar flow up to 1073 K for 3 h. The samples were cooled down to room temperature under Ar and then exposed to air without passivation. MoxC/Al2O3, MoxC/TiO2 and MoxC/SiO2 catalysts with about 26% wt of Mo were prepared by using the proper amount of molybdenum and carbon precursors. A reference catalyst (unsupported), containing only bulk hexagonal Mo2C was prepared following a similar method but in the absence of support [21]. For characterization purposes, the commercial supports were also separately treated up to 1073 K (3 h) under Ar.

2.2. Characterization of Catalysts

The Mo content of samples was determined by inductively coupled plasma mass spectrometry using a Perkin Elmer Optima 3200RL apparatus (Santa Clara, CA, US). The N2 adsorption-desorption isotherms were recorded at 77 K using a Micromeritics Tristar II 3020 equipment. Prior to the measurements, the samples were outgassed at 523 K for 5 h. The specific surface area (SBET) was calculated by multi-point BET analysis of N2 adsorption isotherms. The X-ray powder diffraction (XRD) analysis was performed using a PANalytical X’Pert PRO MPD Alpha1 powder diffractometer (Malvern, UK) equipped with a CuKα1 radiation. The XRD profiles were collected in the 2θ range of 4°–100° with a step size of 0.017° and counting 50 s at each step. Transmission electron microscopy (TEM-HRTEM) images and energy dispersive X-ray analysis (EDX) were collected employing a JEOL J2010F microscope (Tokyo, Japan) operated at an accelerating voltage to 200 kV. The Raman spectra of the samples were collected using a Jobin-Yvon LabRam HR 800, fitted to an optical Olympus BXFM microscope (Kyoto, Japan) with a 532 nm laser and a CCD detector. X-ray photoelectron spectroscopy (XPS) analysis was performed using a Perkin Elmer PHI-5500 Multitechnique System (Physical Electronics, Chanhassen, MN, US) with an Al X-ray source (hυ = 1486.6 eV and 350 W). Samples were kept in an ultra-high vacuum chamber during data acquisition (5·10−9–2·10−8 Torr). Before XPS measurements, the C 1s BE of adventitious carbon was determined in the same equipment and conditions using Au as reference. The BE values were referred to the mentioned C 1s BE at 284.8 eV.

2.3. RWGS Catalytic Tests

The RWGS reaction tests were carried out in a Microactivity-Reference unit (PID Eng&Tech) using a tubular fixed-bed reactor under atmospheric pressure. Approximately, 150 mg of catalyst were diluted with inactive SiC up to 1 mL of catalytic bed. The RWGS was studied at 0.1 MPa, between 548 K and 673 K, by following the temperature sequence: 598 K (3 h)→573 K (3 h)→548 K (10 h)→598 K (3 h)→623 K (3 h)→648 K (3 h)→673 K (3 h)→648 K (5 h). The first part of the catalytic test: 598 K (3 h)→573 K (3 h)→548 K (10 h) was carried out in order to condition the catalyst under RWGS. The gas hourly space velocity (GHSV) was 3000 h−1. The effluent was analysed on-line with a gas chromatograph Varian 450-GC equipped with a methanizer and TCD and FID detectors. CO2 conversion and product distribution at each temperature were determined by the average of at least three measures.

3. Results and Discussion

As stated above, Al2O3-, SiO2- and TiO2-supported MoxC catalysts with about 26% wt Mo were prepared, characterized and tested in the RWGS reaction. Table 1 shows the Mo content and the SBET of fresh catalysts. For comparison, SBET values of the supports treated at 1073 K under Ar, which are the conditions used in the preparation of catalysts, are also included. In all cases, the SBET of the supports after the thermal treatment at 1073 K was lower than that of the corresponding commercial pristine material; the diminution was about 10% for Al2O3 and SiO2, meanwhile for TiO2 the SBET decreased from 117 m2g−1 to 13 m2g−1. For TiO2, a phase change occurred during the thermal treatment; the rutile weight percentage increased from 22% (pristine material) until 95% after the treatment at 1073 K, as determined from XRD analysis [42]. On the other hand, except for the MoxC/TiO2, the SBET of supported catalysts was lower than that of the corresponding support treated at 1073 K; the formation of MoxC could prevent in some extension the surface area decrease of the TiO2 support, which could be related with a different extent of the rutile formation from anatase.
The supported catalysts were analyzed by XRD, and the corresponding XRD patterns are shown in Figure 1, Figure 2 and Figure 3; XRD patterns of the respective supports treated at 1073 K under Ar are also displayed for comparison. From the XRD pattern of MoxC/Al2O3 (Figure 1), characteristic diffraction peaks of γ-Al2O3 are observed, and the main presence of hexagonal Mo2C (JCPDS 00-035-0787) can be deduced; a crystallite size of 28 nm was calculated. The XRD analysis of MoxC/SiO2 (Figure 2) indicates the presence of hexagonal Mo2C; however, the observation of diffraction peaks with maxima at 2θ = 36.9° and 2θ = 42.1° are attributed to the presence of cubic MoC (JCPDS 03-065-0280). From the intensity of diffraction peaks of both phases and that in reference files, a semiquantitative analysis was performed [43]; the presence of 65% cubic MoC and 35% hexagonal Mo2C is determined in the MoxC/SiO2 catalyst. Figure 3 shows the corresponding XRD profile of TiO2-supported catalyst. Characteristic diffraction peaks of both anatase and rutile TiO2 phases are clearly observed. The rutile weight percentage with respect to TiO2 phases calculated from XRD pattern is 51% [42]. As commented above, the formation of MoxC could prevent the anatase transformation, having the MoxC/TiO2 catalyst a higher amount of anatase and a higher surface area than the support treated at 1073 K (Table 1). From the XRD pattern of MoxC/TiO2, the main presence of cubic MoC with poor crystallinity can be proposed, even if the presence of hexagonal Mo2C could not be ruled out (Figure 3).
The catalysts were also characterized by Raman spectroscopy, TEM-HRTEM, STEM-EDX and XPS. Raman spectroscopy was used in order to determine the presence of molybdenum oxide species and/or carbonaceous residues (Figure S1). The very low intensity bands in the zone 815–990 cm−1 points to the presence of residual MoO3 [44,45,46], which could be formed by surface oxidation when the samples were exposed to air. For MoxC/TiO2, Raman bands at 260, 429 and 610 cm−1, assigned to rutile, and at 150 cm−1 assigned to anatase, are clearly visible [47,48,49]. In all cases, the intensity of the bands in the 1200–1700 cm−1 region characteristic of carbonaceous species (D and G bands), is negligible (Figure S1).
TEM-HRTEM and STEM-EDX analysis of MoxC/Al2O3, MoxC/SiO2 and MoxC/TiO2 are shown in Figure 4, Figure 5 and Figure 6, respectively. For MoxC/Al2O3 (Figure 4), the presence of hexagonal Mo2C with a mean particle size of 21 nm was determined in agreement with XRD results. TEM-HRTEM analysis of MoxC/SiO2 (Figure 5) allowed to confirm the presence of hexagonal Mo2C and cubic MoC particles with bimodal distribution and mean particle sizes of 18 nm and 5 nm, respectively (Figure 5A–C). For MoxC/TiO2 (Figure 6), only the presence of the cubic MoC phase with a mean particle size of 4 nm could be determined. The supported MoxC materials studied in this work follow the recently predicted general trend of size-dependent phase diagrams for bulk Mo and W carbides: fcc phases are generally found at small particle size and hcp phases are prevalent at large particle size [50].
In all cases, STEM-EDX results (see Figure 4C, Figure 5D, and Figure 6C) indicate a homogeneous distribution of Mo on the corresponding support. Figure 4D, Figure 5E and Figure 6D, show the corresponding EDX spectra; N- and Cl-containing species were not detected.
As stated above, the catalysts were also analyzed by XPS. Al 2p, Si 2p and Ti 2p3/2 BE at 74.8, 104,0 and 459,3 eV, characteristic of Al2O3, SiO2, and TiO2, were found for MoxC/Al2O3, MoxC/SiO2 and MoxC/TiO2, respectively (Figure S2). Figure 7 shows the C 1s and Mo 3d XP spectra. The C 1s core level spectra (Figure 7A) show a maximum at 284.8 eV associated to the adventitious carbon, the component at 283.7–283.8 eV is associated to surface molybdenum carbide species [21,31,51,52,53,54]. Components extended above 284.8 eV are related to different oxygen containing species [52,53,54,55,56]. The Mo 3d spectra are complex (Figure 7B); however, they can be deconvoluted into four doublets (Mo 3d5/2 and Mo 3d3/2). According to literature, the Mo 3d5/2/Mo 3d3/2 intensity ratio was fixed to be 1.5, and the Mo 3d5/2-Mo 3d3/2 BE splitting was set at 3.1 eV [57,58,59]. The 3d5/2 peaks at the lowest BE region, 228.5–228.7 eV, are attributed to Mo2+ and Mo3+ in Mo2C and/or oxycarbide species [19,21,31,51]. The Mo 3d5/2 components at 229.4–229.5, 231.3–232.6 and 233.2 eV, can be assigned to Mo4+, Mo5+ and Mo6+ surface species, respectively [19,58,59,60,61], which could be related to the presence of MoC, oxycarbide and/or oxide species. Table 2 shows the contribution of Mo2+/Mo3+ and Mo4+ species to the total surface Mon+ species; the MoxC/SiO2 catalyst having both Mo2C and MoC shows the highest values.
All catalysts were tested in the RWGS using CO2:H2 = 1/3 and CO2/H2 = 1/1 ratios. Catalytic data of unsupported Mo2C, prepared using a similar method to that used in this work but in the absence of support, are also included for comparison [21]. As stated in the experimental section, the first part of the catalytic test: 598 K (3 h)→573 K (3 h)→548 K (10 h) was carried out in order to condition the catalyst under RWGS. Next, when the temperature was increased to 598 K, the CO2 conversion was in all cases higher than that obtained at 598 K in the conditioning step (Figure 8A and Figure 10A). This behavior could be related with the removal of initially adsorbed surface species. After this first step and regardless the catalyst and the conditions, CO2 conversion increases with the rising of reaction temperature from 598 K to 673 K (Figure 8A and Figure 10A).
Figure 8 and Figure 9 show the RWGS behavior of catalysts when CO2:H2 = 1/3 is used. MoxC/SiO2 presented the highest value of CO2 conversion (27.5%) at 673 K (Figure 8A); the corresponding equilibrium CO2 conversion for RWGS at the experimental conditions used is about 37% (at 673 K). MoxC/Al2O3 showed a catalytic activity close to that of the unsupported Mo2C catalyst. Meanwhile, MoxC/TiO2 showed lower values of CO2 conversion than those of unsupported Mo2C [21]. These results contrast with those usually reported for supported metallic catalysts [62,63]. The activity of SiO2- and Al2O3-supported metals in the RWGS is usually lower than that found when reducible supports such as TiO2 or CeO2 are used, which can generate oxygen vacancies that strengths the CO2 adsorption and then the activity in the RWGS [63]. In this work, besides the difference in the surface-area of catalysts, the composition and characteristics of generated MoxC nanoparticles change as a function of the support.
A key process in the RWGS is the cleavage of C-O bond with CO + O formation. In this context molybdenum oxycarbide has been proposed as an intermediate in the RWGS over Mo2C that likely enhances the RWGS rate [25]. We have demonstrated that over a polycrystalline α-Mo2C catalyst, prepared with the method used in the present work, the enhanced CO2 dissociation toward CO + O results from specific surface facets [21]. Next, the easy release of CO and the continuous O removal by H2 to form H2O, results in high RWGS activity. The existence of both, hcp Mo2C and fcc MoC phases in the SiO2-supported catalyst, could result in interphases regions with appropriate characteristics to enhance RWGS on MoxC/SiO2 catalyst. In this context, for different MoxC bulk catalysts, the lowest activation energy in the RWGS was found for a catalyst containing several Mo2C and MoC phases [31].
All the supported catalysts showed high CO selectivity values. When CO2:H2 = 1/3 was used, CO selectivity were always higher than 92% (Figure 8B). The highest CO selectivity was observed for the MoxC/SiO2 catalyst, achieving at 673 K, 98.5%. Only MoxC/Al2O3 showed CO selectivity values slightly lower than that of unsupported Mo2C (Figure 8B). CH4 was the main byproduct and only very small amounts of ethylene were formed.
For a proper comparison of the catalysts, the values of CO production were calculated per mol of Mo in the samples; results are shown in Figure 9. All the supported catalysts showed a higher CO production per mol of Mo compared to the unsupported Mo2C catalyst [21]. At the end of the catalytic test, MoxC/SiO2 and MoxC/Al2O3 showed a higher CO production at 648 K than before reaction at 673 K (Figure 9). This could be related with the removal of remaining oxygen surface species during the reaction at 673 K. The highest CO production in the whole range of reaction temperature tested was obtained for MoxC/SiO2; it reached about 17.0 mol CO/mol Mo·h at 673 K.
Catalysts were also tested in the RWGS using a stoichiometric ratio of the reactant mixture, CO2/H2/ = 1/1. Figure 10 shows the variation of CO2 conversion and CO selectivity values. As expected, the CO2 conversion (Figure 10A) was lower and the CO selectivity (Figure 10B) higher when a mixture CO2/H2 = 1/1 was used than when the reactant mixture was CO2/H2 = 1/3. Using the CO2/H2 = 1/1 reactant mixture, the highest CO2 conversion (Figure 10A) and the highest CO production per mol of Mo (Figure 11), in the whole range of reaction temperature tested, were also found over the MoxC/SiO2 catalyst. In this case, at the end of the catalytic test, only for MoxC/SiO2 a slightly higher CO production at 648 K than before reaction at 673 K was observed (Figure 11).
It is noteworthy, that after the overall RWGS study carried out, all supported catalysts, showed quite constant values of CO2 conversion and CO selectivity during the last step at 648 K (5 h), under both CO2/H2/ = 1/3 and CO2/H2/ = 1/1 conditions.
The apparent activation energies (Ea) for CO production over supported catalysts were calculated according to the Arrhenius plots in the temperature range of 598–648 K; values between 65–78 kJ/mol were obtained (Table 2). These values are in the range of that recently reported for an alumina supported Mo2C cluster-based catalyst (76.4 kJ/mol) [39]. MoxC/SiO2 showed the lowest Ea for CO production. As stated above, the best performance of MoxC/SiO2 could be related with the coexistence in this catalyst of different MoxC phases, hexagonal Mo2C and cubic MoC, as has been recently suggested for unsupported MoxC catalysts [31]. Moreover, MoxC/SiO2 showed the highest contribution of Mo2+/Mo3+ and Mo4+ species to the total surface Mon+ species. For MoxC-based catalysts, an easy reduction under reaction conditions of molybdenum species has been related with their performance in RWGS [41].
Post-reaction catalysts were characterized by BET and XRD. Only a slight decrease in the BET surface area was found after the RWGS reaction (Table 1). The XRD patterns of fresh (Figure 1, Figure 2 and Figure 3) and post-reaction catalysts after the test with CO2/H2 = 1/3 (Figure S3) were similar. Meanwhile, the presence of MoO2 was detected by XRD in post-reaction MoxC/SiO2 and MoxC/TiO2 when the reactant mixture was CO2/H2 = 1/1 (Figure S4); the oxidation could be prevented under a richer hydrogen atmosphere (CO2/H2 = 1/3) due to an easier removal of the O surface species formed from the CO2 activation over these materials under CO2/H2 = 1/3 conditions [21,31].

4. Conclusions

Using urea and MoCl5 as carbon and molybdenum sources, different MoxC phases were successfully supported over Al2O3, SiO2 and TiO2. The support determined the developed MoxC phases on the materials and their catalytic behavior in the RWGS. Hexagonal Mo2C nanoparticles on MoxC/Al2O3 and cubic MoC nanoparticles on MoxC/TiO2 were found. Over MoxC/SiO2 both hexagonal Mo2C and cubic MoC nanoparticles were present. In all cases, supported hexagonal Mo2C nanoparticles were larger than cubic MoC ones.
All catalysts showed a stable catalytic behavior and exhibited higher CO production per mol of Mo than the unsupported hexagonal Mo2C similarly prepared, under the reaction conditions used (CO2/H2 = 1/3 and CO2/H2 = 1/1; T = 548–673 K).
MoxC/SiO2 exhibited the highest surface ratio of Mo species with low oxidation states (Mo2+,3+,4+) and the best performance in the RWGS reaction. Over MoxC/SiO2, CO2 conversion of 27.5% and CO selectivity of 98.5% were achieved at 673 K under CO2/H2 = 1/3; for CO production, an apparent activation energy of 64.9 ± 3.2 kJ mol−1 was determined at 598–648 K under CO2/H2 = 1/1. The catalytic behavior is proposed to be governed by the supported MoxC phase. The simultaneous presence of hexagonal Mo2C and cubic MoC nanoparticles in MoxC/SiO2 plays a main role on the catalytic behavior of this catalyst.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/nano12183165/s1, Figure S1. Raman spectra of fresh MoxC/support catalysts; Figure S2. XP spectra of MoxC/support catalysts. (A) Al 2p level registered for MoxC/Al2O3, (B) Si 2p level registered for MoxC/SiO2, (C) Ti 2p level registered for MoxC/TiO2; Figure S3. XRD patterns of MoxC/support catalysts after RWGS reaction (CO2/H2 = 1/3); reaction conditions: mcat = 150 mg, GHSV = 3000 h−1, P = 0.1 MPa.; Figure S4. XRD patterns of MoxC/support catalysts after RWGS reaction (CO2/H2 = 1/1); reaction conditions: mcat = 150 mg, GHSV = 3000 h−1, P = 0.1 MPa.

Author Contributions

Methodology, experimental and formal analysis A.P., X.L., J.R.B., P.R.d.l.P. and N.H.; writing—original draft, A.P., X.L., P.R.d.l.P. and N.H.; writing—review and editing, A.P., P.R.d.l.P. and N.H.; supervision, P.R.d.l.P. and N.H.; project administration and funding acquisition, P.R.d.l.P. and N.H. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by MAT2017-87500-P and PID2020-116031RB I00/AEI/10.13039/501100011033/FEDER projects.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data present in this study are available on request from the corresponding author.

Acknowledgments

The authors thank MAT2017-87500-P and PID2020-116031RB I00/AEI/10.13039/501100011033/FEDER projects, for financial support. JR.B. acknowledges the Spanish SECAT for his master thesis grant. X.L. is grateful to the China Scholarship Council and the University of Barcelona (IN2UB) for her PhD grants. A.P. thanks MINECO for his PhD grant (BES-C-2015-074574).

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Leung, D.Y.C.; Caramanna, G.; Maroto-Valer, M.M. An Overview of Current Status of Carbon Dioxide Capture and Storage Technologies. Renew. Sustain. Energy Rev. 2014, 39, 426–443. [Google Scholar] [CrossRef]
  2. Cuéllar-Franca, R.M.; Azapagic, A. Carbon Capture, Storage and Utilisation Technologies: A Critical Analysis and Comparison of Their Life Cycle Environmental Impacts. J. CO2 Util. 2015, 9, 82–102. [Google Scholar] [CrossRef]
  3. Choi, S.; Drese, J.H.; Jones, C.W. Adsorbent Materials for Carbon Dioxide Capture from Large Anthropogenic Point Sources. Chem. Sus. Chem. 2009, 2, 796–854. [Google Scholar] [CrossRef] [PubMed]
  4. D'Alessandro, D.M.; Smit, B.; Long, J.R. Carbon Dioxide Capture: Prospects for New Materials. Angew. Chem. Int. Ed. Engl. 2010, 49, 6058–6082. [Google Scholar] [CrossRef] [PubMed]
  5. Homs, N.; Toyir, J.; Ramirez de la Piscina, P. Catalytic Processes for Activation of CO2. In New and Future Developments in Catalysis; Elsevier: Amsterdam, The Netherlands, 2013; pp. 1–26. [Google Scholar]
  6. Din, I.U.; Shaharun, M.S.; Alotaibi, M.A.; Alharthi, A.I.; Naeem, A. Recent Developments on Heterogeneous Catalytic CO2 Reduction to Methanol. J. CO2 Util. 2019, 34, 20–33. [Google Scholar]
  7. Saeidi, S.; Najari, S.; Hessel, V.; Wilson, K.; Keil, F.J.; Concepción, P.; Suib, S.L.; Rodrigues, A.E. Recent Advances in CO2 Hydrogenation to Value-Added Products-Current Challenges and Future Directions. Prog. Energy Combust. 2021, 85, 100905. [Google Scholar]
  8. Bahmanpour, A.M.; Signorile, M.; Kröcher, O. Recent Progress in Syngas Production Via Catalytic CO2 Hydrogenation Reaction. Appl. Catal. B 2021, 295, 120319. [Google Scholar] [CrossRef]
  9. Boot-Handford, M.E.; Abanades, J.C.; Anthony, E.J.; Blunt, M.J.; Brandani, S.; Mac Dowell, N.; Fernández, J.R.; Ferrari, M.C.; Gross, R.; Hallett, J.P.; et al. Carbon Capture and Storage Update. Energy Environ. Sci. 2014, 7, 130–189. [Google Scholar]
  10. Daza, Y.A.; Kuhn, J.N. CO2 Conversion by Reverse Water Gas Shift Catalysis: Comparison of Catalysts, Mechanisms and Their Consequences for CO2 Conversion to Liquid Fuels. RSC Adv. 2016, 6, 49675–49691. [Google Scholar] [CrossRef]
  11. Liu, X.M.; Lu, G.Q.; Yan, Z.F.; Beltramini, J. Recent Advances in Catalysts for Methanol Synthesis Via Hydrogenation of CO and CO2. Ind. Eng. Chem. Res. 2003, 42, 6518–6530. [Google Scholar] [CrossRef]
  12. Jahangiri, H.; Bennett, J.; Mahjoubi, P.; Wilson, K.; Gu, S. A Review of Advanced Catalyst Development for Fischer–Tropsch Synthesis of Hydrocarbons from Biomass Derived Syn-Gas. Catal. Sci. Technol. 2014, 4, 2210–2229. [Google Scholar] [CrossRef]
  13. Saeidi, S.; Amin, N.A.S.; Rahimpour, M.R. Hydrogenation of CO2 to Value-Added Products—A Review and Potential Future Developments. J. CO2 Util. 2014, 5, 66–81. [Google Scholar] [CrossRef]
  14. Elsernagawy, O.Y.H.; Hoadley, A.; Patel, J.; Bhatelia, T.; Lim, S.; Haque, N.; Li, C. Thermo-Economic Analysis of Reverse Water-Gas Shift Process With Different Temperatures for Green Methanol Production as a Hydrogen Carrier. J. CO2 Util. 2020, 41, 101280. [Google Scholar] [CrossRef]
  15. Kirsch, H.; Sommer, U.; Pfeifer, P.; Dittmeyer, R. Power-To-Fuel Conversion Based on Reverse Water-Gas-Shift, Fischer-Tropsch Synthesis and Hydrocracking: Mathematical Modeling and Simulation in Matlab/Simulink. Chem. Eng. Sci. 2020, 227, 115930. [Google Scholar] [CrossRef]
  16. Liang, B.; Duan, H.; Su, X.; Chen, X.; Huang, Y.; Chen, X.; Delgado, J.J.; Zhang, T. Promoting Role of Potassium in the Reverse Water Gas Shift Reaction on Pt/Mullite Catalyst. Catal. Today 2017, 281, 319–326. [Google Scholar] [CrossRef]
  17. Levy, R.B.; Boudart, M. Platinum-Like Behavior of Tungsten Carbide in Surface Catalysis. Science 1973, 181, 547–549. [Google Scholar] [CrossRef] [PubMed]
  18. Oyama, S.T. The Chemistry of Transition Metal Carbides and Nitrides; Blackie Academic & Professional: Glasgow, Scotland, 1996. [Google Scholar]
  19. Porosoff, M.D.; Yang, X.; Boscoboinik, J.A.; Chen, J.G. Molybdenum Carbide as Alternative Catalysts to Precious Metals for Highly Selective Reduction of CO2 to CO. Angew. Chem. Int. Ed. Engl. 2014, 53, 6705–6709. [Google Scholar] [CrossRef]
  20. Porosoff, M.D.; Kattel, S.; Li, W.; Liu, P.; Chen, J.G. Identifying Trends and Descriptors for Selective CO2 Conversion to CO Over Transition Metal Carbides. Chem. Commun. 2015, 51, 6988–6991. [Google Scholar] [CrossRef]
  21. Liu, X.; Kunkel, C.; Ramírez de la Piscina, P.; Homs, N.; Viñes, F.; Illas, F. Effective and Highly Selective CO Generation from CO2 Using a Polycrystalline α-Mo2C Catalyst. ACS Catal. 2017, 7, 4323–4335. [Google Scholar] [CrossRef]
  22. Pajares, A.; Prats, H.; Romero, A.; Viñes, F.; de la Piscina, P.; Sayós, R.; Homs, N.; Illas, F. Critical Effect of Carbon Vacancies on the Reverse Water Gas Shift Reaction over Vanadium Carbide Catalysts. Appl. Catal. B 2020, 267, 118719. [Google Scholar] [CrossRef]
  23. Kunkel, C.; Viñes, F.; Illas, F. Transition metal carbides as novel materials for CO2 capture, storage, and activation. Energy Environ. Sci. 2016, 9, 141–144. [Google Scholar] [CrossRef]
  24. Posada-Pérez, S.; Viñes, F.; Ramirez, P.J.; Vidal, A.B.; Rodriguez, J.A.; Illas, F. The bending machine: CO2 activation and hydrogenation on δ-MoC(001) and β-Mo2C(001) surfaces. Phys. Chem. Chem. Phys. 2014, 16, 14912–14921. [Google Scholar] [CrossRef] [PubMed]
  25. Reddy, K.P.; Dama, S.; Mhamane, N.B.; Ghosalya, M.K.; Raja, T.; Satyanarayana, C.V.; Gopinath, C.S. Molybdenum carbide catalyst for the reduction of CO2 to CO: Surface science aspects by NAPPES and catalysis studies. Dalton Trans. 2019, 48, 12199–12209. [Google Scholar] [CrossRef]
  26. Claridge, J.B.; York, A.P.E.; Brungs, A.J.; Green, M.L.H. Study of the Temperature-Programmed Reaction Synthesis of Early Transition Metal Carbide and Nitride Catalyst Materials from Oxide Precursors. Chem. Mater. 2000, 12, 132–142. [Google Scholar] [CrossRef]
  27. Volpe, L.; Boudart, M. Compounds of Molybdenum and Tungsten with High Specific Surface Area. J. Solid State Chem. 1985, 59, 348–356. [Google Scholar] [CrossRef]
  28. Naito, S.; Tsuji, M.; Sakamoto, Y.; Miyao, T. Marked Difference of Catalytic Behavior by Preparation Methods in CH4 Reforming with CO2 Over Mo2C and WC Catalysts. Stud. Surf. Sci. Catal. 2000, 143, 415–423. [Google Scholar]
  29. Giordano, C.; Erpen, C.; Yao, W.; Antonietti, M. Synthesis of Mo and W Carbide and Nitride Nanoparticles Via a Simple “Urea Glass” Route. Nano Lett. 2008, 8, 4659–4663. [Google Scholar] [CrossRef]
  30. Gao, J.; Wu, Y.; Jia, C.; Zhong, Z.; Gao, F.; Yang, Y.; Liu, B. Controllable Synthesis of α-MoC1-X and β-Mo2C Nanowires for Highly Selective CO2 Reduction to CO. Catal. Commun. 2016, 84, 147–150. [Google Scholar] [CrossRef]
  31. Liu, X.; Pajares, A.; Matienzo, D.D.C.; Ramírez de la Piscina, P.; Homs, N. Preparation and Characterization of Bulk MoxC Catalysts and Their Use in the Reverse Water-Gas Shift Reaction. Catal. Today 2020, 356, 384–389. [Google Scholar] [CrossRef]
  32. Tsuji, M.; Miyao, T.; Naito, S. Remarkable Support Effect of ZrO2 Upon the CO2 Reforming of CH4 Over Supported Molybdenum Carbide Catalysts. Catal. Lett. 2000, 60, 195–198. [Google Scholar] [CrossRef]
  33. Chen, X.; Zhang, T.; Ying, P.; Zheng, M.; Wu, W.; Xia, L.; Li, T.; Wang, X.; Li, C. A Novel Catalyst for Hydrazine Decomposition: Molybdenum Carbide Supported on γ-Al2O3. Chem. Commun. 2002, 3, 288–289. [Google Scholar] [CrossRef] [PubMed]
  34. Aegerter, P.A.; Quigley, W.W.C.; Simpson, G.J.; Ziegler, D.D.; Logan, J.W.; McCrea, K.R.; Glazier, S.; Bussell, M.E. Thiophene Hydrodesulfurization over Alumina-Supported Molybdenum Carbide and Nitride Catalysts: Adsorption Sites, Catalytic Activities, and Nature of the Active Surface. J. Catal. 1996, 164, 109–121. [Google Scholar] [CrossRef]
  35. Da Costa, P.; Potvin, C.; Manoli, J.M.; Breysse, M.; Djéga-Mariadassou, G. Novel Phosphorus-Doped Alumina-Supported Molybdenum and Tungsten Carbides: Synthesis, Characterization and Hydrogenation Properties. Catal. Lett. 2001, 72, 91–97. [Google Scholar] [CrossRef]
  36. Vo, D.N.; Adesina, A.A. Fischer–Tropsch Synthesis over Alumina-Supported Molybdenum Carbide Catalyst. Appl. Catal. A Gen. 2011, 399, 221–232. [Google Scholar] [CrossRef]
  37. Nagai, M.; Kurakami, T. Reverse Water Gas Shift Reaction Over Molybdenum Carbide. J. Chem. Eng. Jpn. 2005, 38, 807–812. [Google Scholar] [CrossRef]
  38. Porosoff, M.D.; Baldwin, J.W.; Peng, X.; Mpourmpakis, G.; Willauer, H.D. Potassium-Promoted Molybdenum Carbide as a Highly Active and Selective Catalyst for CO2 Conversion to CO. Chem. Sus. Chem. 2017, 10, 2408–2415. [Google Scholar] [CrossRef] [PubMed]
  39. Ma, Y.; Guo, Z.; Jiang, Q.; Wu, K.; Gong, H.; Liu, Y. Molybdenum Carbide Clusters for Thermal Conversion of CO2 to CO Via Reverse Water-Gas Shift Reaction. J. Energy Chem. 2020, 50, 37–43. [Google Scholar] [CrossRef]
  40. Marquart, W.; Raseale, S.; Prieto, G.; Zimina, A.; Sarma, B.B.; Grunwaldt, J.-D.; Claeys, M.; Fischer, N. CO2 Reduction over Mo2C-Based Catalysts. ACS Catal. 2021, 11, 1624–1639. [Google Scholar] [CrossRef]
  41. Juneau, M.; Pope, C.; Liu, R.; Porosoff, M.D. Support Acidity as a Descriptor for Reverse Water-Gas Shift over Mo2C-Based Catalysts. Appl. Catal. A Gen. 2021, 620, 118034. [Google Scholar] [CrossRef]
  42. Zhang, H.; Banfield, J.F. Understanding Polymorphic Phase Transformation Behavior During Growth of Nanocrystalline Aggregates: Insights from TiO2. J. Phys. Chem. B 2000, 104, 3481–3487. [Google Scholar] [CrossRef]
  43. Snyder, R.L. The use of reference intensity ratios in X-ray quantitative analysis. Powder Diffr. 1992, 7, 186–193. [Google Scholar] [CrossRef]
  44. Dieterle, M.; Weinberg, G.; Mestl, G. Raman Spectroscopy of Molybdenum Oxides. Part I. Structural Characterization of Oxygen Defects in MoO1-x by DR UV/VIS, Raman Spectroscopy and X-Ray Diffraction. Phys. Chem. Chem. Phys. 2002, 4, 812–821. [Google Scholar] [CrossRef]
  45. Silveira, J.V.; Batista, J.A.; Saraiva, G.D.; Mendes Filho, J.; Souza Filho, A.G.; Hu, S.; Wang, X. Temperature Dependent Behavior of Single Walled MoO3 Nanotubes: A Raman Spectroscopy Study. Vib. Spectrosc. 2010, 54, 179–183. [Google Scholar] [CrossRef]
  46. Camacho-López, M.; Escobar-Alarcón, L.; Picquart, M.; Arroyo, R.; Córdoba, G.; Haro-Poniatowski, E. Micro-Raman Study of the m-MoO2 to α-MoO3. Opt. Mater. 2011, 33, 480–484. [Google Scholar] [CrossRef]
  47. Zhang, W.; He, Y.; Zhang, M.; Yin, Z.; Chen, Q. Raman Scattering Study on Anatase TiO2 nanocrystals. J. Phys. D Appl. Phys. 2000, 33, 912–916. [Google Scholar] [CrossRef]
  48. Suo, Z.; Kou, Y.; Niu, J.Z.; Zhang, W.Z.; Wang, H.I. Characterization of TiO2-, ZrO2- and Al2O3-Supported Iron Catalysts as Used for CO2 Hydrogenation. Appl. Catal. A Gen. 1997, 148, 301–313. [Google Scholar] [CrossRef]
  49. Mazza, T.; Barborini, E.; Piseri, P.; Milani, P.; Cattaneo, D.; Li Bassi, A.; Bottani, C.E.; Ducati, C. Raman Spectroscopy Characterization of TiO2 Rutile Nanocrystals. Phys. Rev. B 2007, 75, 045416. [Google Scholar] [CrossRef]
  50. Shrestha, A.; Gao, X.; Hicks, J.C.; Paolucci, C. Nanoparticle Size Effects on Phase Stability for Molybdenum and Tungsten Carbides. Chem. Mater. 2021, 33, 4606–4620. [Google Scholar] [CrossRef]
  51. Gao, Q.; Zhao, X.; Xiao, Y.; Zhao, D.; Cao, M. A Mild Route to Mesoporous Mo2C–C Hybrid Nanospheres for High Performance Lithium-Ion Batteries. Nanoscale 2014, 6, 6151. [Google Scholar] [CrossRef]
  52. Zhu, Y.; Wang, S.; Zhong, Y.; Cai, R.; Li, L.; Shao, Z. Facile Synthesis of a MoO2–Mo2C–C Composite and Its Application as Favorable Anode Material for Lithium-Ion Batteries. J. Power Sources 2016, 307, 552–560. [Google Scholar] [CrossRef]
  53. Ojha, K.; Saha, S.; Kolev, H.; Kumar, B.; Ganguli, A.K. Composites of Graphene-Mo2C Rods: Highly Active and Stable Electrocatalyst for Hydrogen Evolution Reaction. Electrochim. Acta 2016, 193, 268–274. [Google Scholar]
  54. Li, R.; Wang, S.; Wang, W.; Cao, M. Ultrafine Mo2C Nanoparticles Encapsulated in N-Doped Carbon Nanofibers with Enhanced Lithium Storage Performance. Phys. Chem. Chem. Phys. 2015, 17, 24803–24809. [Google Scholar] [CrossRef] [PubMed]
  55. Bhaskar, A.; Deepa, M.; Narasinga Rao, T.N. MoO2/Multiwalled Carbon Nanotubes (MWCNT) Hybrid for Use as a Li-Ion Battery Anode. ACS Appl. Mater. Interfaces 2013, 5, 2555–2566. [Google Scholar] [CrossRef] [PubMed]
  56. Chen, M.; Liu, J.; Zhou, W.; Lin, J.; Shen, Z. Nitrogen-Doped Graphene-Supported Transition-Metals Carbide Electrocatalysts for Oxygen Reduction Reaction. Sci. Rep. 2015, 5, 10389–10398. [Google Scholar]
  57. Ji, W.; Shen, R.; Yang, R.; Yu, G.; Guo, X.; Peng, L.; Ding, W. Partially Nitride Molybdenum Trioxide With Promoted Performance as an Anode Material for Lithium-Ion Batteries. J. Mater. Chem. A 2014, 2, 699–704. [Google Scholar] [CrossRef]
  58. Spevack, P.A.; McIntyre, N.S. A Raman and XPS Investigation of Supported Molybdenum Oxide Thin Films. 1. Calcination and Reduction Studies. J. Phys Chem. 1993, 97, 11020–11030. [Google Scholar] [CrossRef]
  59. Oshikawa, K.; Nagai, M.; Omi, S. Characterization of Molybdenum Carbides for Methane Reforming by TPR, XRD, and XPS. J. Phys. Chem. B 2001, 105, 9124–9131. [Google Scholar] [CrossRef]
  60. Guil-López, R.; Nieto, E.; Botas, J.A.; Fierro, J.L.G. On the Genesis of Molybdenum Carbide Phases During Reduction-Carburization Reactions. J. Solid State Chem. 2012, 190, 285–295. [Google Scholar] [CrossRef]
  61. Ma, Y.; Guan, G.; Hao, X.; Zuo, Z.; Huang, W.; Phanthong, P.; Kusakabe, K.; Abudula, A. Highly-Efficient Steam Reforming of Methanol over Copper Modified Molybdenum Carbide. RSC Adv. 2014, 4, 44175–44184. [Google Scholar] [CrossRef]
  62. Su, X.; Yang, X.; Zhao, B.; Huang, Y. Designing of highly selective and high-temperature endurable RWGS heterogeneous catalysts: Recent advances and the future directions. J. Energy Chem. 2017, 26, 854–867. [Google Scholar] [CrossRef]
  63. Zhu, M.; Ge, Q.; Zhu, X. Catalytic Reduction of CO2 to CO via Reverse Water Gas Shift Reaction: Recent Advances in the Design of Active and Selective Supported Metal Catalysts. Trans. Tianjin Univ. 2020, 26, 172–187. [Google Scholar] [CrossRef] [Green Version]
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Figure 1. XRD patterns of MoxC/Al2O3 catalyst and the Al2O3 support after thermal treatment at 1073 K.
Figure 1. XRD patterns of MoxC/Al2O3 catalyst and the Al2O3 support after thermal treatment at 1073 K.
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Figure 2. XRD patterns of MoxC/SiO2 catalyst and the SiO2 support after thermal treatment at 1073 K.
Figure 2. XRD patterns of MoxC/SiO2 catalyst and the SiO2 support after thermal treatment at 1073 K.
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Figure 3. XRD patterns of MoxC/TiO2 catalyst and the TiO2 support after thermal treatment at 1073 K.
Figure 3. XRD patterns of MoxC/TiO2 catalyst and the TiO2 support after thermal treatment at 1073 K.
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Figure 4. (A,B) TEM−HRTEM micrographs of MoxC/Al2O3 catalyst; (C) STEM−EDX mapping; (D) EDX spectrum.
Figure 4. (A,B) TEM−HRTEM micrographs of MoxC/Al2O3 catalyst; (C) STEM−EDX mapping; (D) EDX spectrum.
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Figure 5. (A–C) TEM−HRTEM micrographs of MoxC/SiO2 catalyst; (D) STEM−EDX mapping; (E) EDX spectrum.
Figure 5. (A–C) TEM−HRTEM micrographs of MoxC/SiO2 catalyst; (D) STEM−EDX mapping; (E) EDX spectrum.
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Figure 6. (A,B) TEM−HRTEM micrographs of MoxC/TiO2 catalyst; (C) STEM−EDX mapping; (D) EDX spectrum.
Figure 6. (A,B) TEM−HRTEM micrographs of MoxC/TiO2 catalyst; (C) STEM−EDX mapping; (D) EDX spectrum.
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Figure 7. XP spectra of MoxC/support catalysts: (A) C 1s level; (B) Mo 3d level.
Figure 7. XP spectra of MoxC/support catalysts: (A) C 1s level; (B) Mo 3d level.
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Figure 8. Catalytic behavior of MoxC/support and unsupported reference Mo2C catalysts in the RWGS reaction as a function of reaction temperature; (A) CO2 conversion, (B) CO selectivity. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/3/1, GHSV = 3000 h−1, P = 0.1 MPa.
Figure 8. Catalytic behavior of MoxC/support and unsupported reference Mo2C catalysts in the RWGS reaction as a function of reaction temperature; (A) CO2 conversion, (B) CO selectivity. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/3/1, GHSV = 3000 h−1, P = 0.1 MPa.
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Figure 9. CO production per mol of Mo as a function of reaction temperature in RWGS over MoxC/support and unsupported reference Mo2C catalysts. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/3/1, GHSV = 3000 h−1, P = 0.1 MPa.
Figure 9. CO production per mol of Mo as a function of reaction temperature in RWGS over MoxC/support and unsupported reference Mo2C catalysts. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/3/1, GHSV = 3000 h−1, P = 0.1 MPa.
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Figure 10. Catalytic behavior of MoxC/support and unsupported reference Mo2C catalysts in the RWGS reaction as a function of reaction temperature; (A) CO2 conversion, (B) CO selectivity. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/1/3, GHSV = 3000 h−1, P = 0.1 MPa.
Figure 10. Catalytic behavior of MoxC/support and unsupported reference Mo2C catalysts in the RWGS reaction as a function of reaction temperature; (A) CO2 conversion, (B) CO selectivity. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/1/3, GHSV = 3000 h−1, P = 0.1 MPa.
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Figure 11. CO production per mol Mo as a function of reaction temperature in RWGS over MoxC/support and unsupported reference Mo2C catalysts. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/1/3, GHSV = 3000 h−1, P = 0.1 MPa.
Figure 11. CO production per mol Mo as a function of reaction temperature in RWGS over MoxC/support and unsupported reference Mo2C catalysts. Reaction conditions: mcat = 150 mg, CO2/H2/N2 = 1/1/3, GHSV = 3000 h−1, P = 0.1 MPa.
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Table
Table 1. Mo content, determined by chemical analysis and surface area (SBET) of fresh and post-reaction catalysts.
Table 1. Mo content, determined by chemical analysis and surface area (SBET) of fresh and post-reaction catalysts.
CatalystMo (%wt)SBET (m2 g−1)
Fresh aPost-Reaction bPost-Reaction c
MoxC/Al2O325.1119 (204)9397
MoxC/SiO225.5129 (181)115107
MoxC/TiO227.539 (13)3225
a between brackets SBET of supports treated at 1073 K; b CO2/H2/N2 = 1/3/1 reactant mixture; c CO2/H2/N2 = 1/1/3 reactant mixture.
Table
Table 2. Apparent Ea determined for MoxC/support catalysts and surface characteristics determined from XPS.
Table 2. Apparent Ea determined for MoxC/support catalysts and surface characteristics determined from XPS.
CatalystEa (kJ·mol−1)(Mo2+,3+/Total Mon+)XPS(Mo2+,3+,4+/Total Mon+)XPS
MoxC/Al2O377.7 ± 1.70.2770.347
MoxC/SiO264.9 ± 3.20.4310.690
MoxC/TiO277.9 ± 4.10.0980.316
Reaction conditions: CO2/H2/N2 = 1/1/3, GHSV = 3000 h−1, P = 0.1 MPa and T = 598–648 K.
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Pajares, A.; Liu, X.; Busacker, J.R.; Ramírez de la Piscina, P.; Homs, N. Supported Nanostructured MoxC Materials for the Catalytic Reduction of CO2 through the Reverse Water Gas Shift Reaction. Nanomaterials 2022, 12, 3165. https://doi.org/10.3390/nano12183165

AMA Style

Pajares A, Liu X, Busacker JR, Ramírez de la Piscina P, Homs N. Supported Nanostructured MoxC Materials for the Catalytic Reduction of CO2 through the Reverse Water Gas Shift Reaction. Nanomaterials. 2022; 12(18):3165. https://doi.org/10.3390/nano12183165

Chicago/Turabian Style

Pajares, Arturo, Xianyun Liu, Joan R. Busacker, Pilar Ramírez de la Piscina, and Narcís Homs. 2022. "Supported Nanostructured MoxC Materials for the Catalytic Reduction of CO2 through the Reverse Water Gas Shift Reaction" Nanomaterials 12, no. 18: 3165. https://doi.org/10.3390/nano12183165

APA Style

Pajares, A., Liu, X., Busacker, J. R., Ramírez de la Piscina, P., & Homs, N. (2022). Supported Nanostructured MoxC Materials for the Catalytic Reduction of CO2 through the Reverse Water Gas Shift Reaction. Nanomaterials, 12(18), 3165. https://doi.org/10.3390/nano12183165

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