Promoting CO2 hydrogenation to methanol by incorporating adsorbents into catalysts: Effects of hydrotalcite
Introduction
Recent reports have heightened the urgency of immediate action to keep the global average temperature rise within 2 K due to current high and increasing CO2 emissions [1]. Considerable efforts have been made to ease the crisis by reducing usage of fossil fuels, but challenges still exist in reducing the great amount of CO2 produced from industry [2], [3]. An attractive strategy, with the continuously reducing cost of hydrogen production, is highlighted recently to convert CO2 and H2 to value-added chemicals (methanol, hydrocarbons, etc.) in the presence of catalysts, where CO2 to methanol (MeOH) is one of the cornerstones of these processes [4], [5]. The produced methanol can not only be directly used as a fuel or additive, but can also be further converted into other chemicals, converting the low energy density of H2 and reducing the emissions of CO2 [6], [7], [8].
Significant as it is, nevertheless, intractable problems remain to be solved to date. One of the most significant restrictions lies in the thermodynamic equilibrium. As the synthesis of methanol will be promoted at high pressure and low temperature, strict reaction conditions are required to attain acceptable methanol yields [9]. However, the equilibrium CO2 conversion and methanol selectivity remain at 26.6% and 71.6%, respectively, even at industrially relevant conditions of 523 K and 5.0 MPa. Poor catalytic activity of conventional catalysts also exists. To improve the methanol formation rate and methanol selectivity, modification and improvement of copper-based catalysts has taken place for decades. As shown in Table 1, copper-based catalysts derived from co-precipitation still dominate in CO2 hydrogenation. In traditional copper-based catalyst systems such as typical Cu-ZnO-Al2O3 and Cu-ZnO-ZrO2, ZnO serves as a physical spacer between copper particles and helps disperse copper particles and promote their activities [10], [11], [12], [13]; Al2O3 and ZrO2 benefit the stability of active copper [11], [14], [15]. Additionally, many transition metals are used to improve the catalytic activity in CO2 hydrogenation. Widely applied options include cerium (Ce), manganese (Mn), lanthanum (La), etc., which can fine-tune the metal-oxide interfaces efficiently [16], [17], [18], [19] Recently, many non-copper-based catalysts have also been developed, e.g., replacing copper with noble or rare metals as active components [20], [21], [22], achieving significant improvements in CO2 conversion and methanol selectivity. However, the high costs in the preparations of noble catalysts is an economic barrier for their application in industry. Alternatively, one straightforward means to enhance methanol synthesis is elevating reaction pressure at the expense of increased energy consumption [23].
To avoid the additional operation cost from elevating total system pressure, a novel strategy is to increase CO2 partial pressure to combine the catalyst with a CO2 adsorbent. Specifically, CO2 as a reactant can be adsorbed on the added adsorbent during the catalytic reaction, so that the CO2 concentration directly adjacent to the active catalytic site increases, which is equivalent to an elevated partial pressure of CO2 in the reaction system. For this purpose, Mg-Al types of hydrotalcite (HT) was adopted as a candidate as it possesses remarkable adsorption capacities for CO2 within the temperature range of methanol synthesis between 473 and 523 K [32], [33], [34]. Hydrotalcite consists of layered double hydroxides and presents a BET surface area of about 200 m2 g−1 after activation with favorable properties for CO2 adsorption though not for methanol production. This method may be applied in catalytic reactions where CO2 is involved as a reactant regardless of catalyst type.
In the present work, the commercial copper-based methanol catalyst (denoted CZA here) and high-temperature CO2 adsorbent hydrotalcite (denoted HT here) were used to confirm and investigate the influence of an imported adsorbent into the process of CO2 hydrogenation to methanol. A series of CZA-HT samples with incremental HT contents were prepared by physical mixing at a powder level, with subsequent pelleting, and thus the effect of CO2 adsorption on the catalytic performance can be assessed. CZA and HT were characterized by TGA, XRD, SEM, N2 physisorption, H2-TPR and N2O titration, and CO2 adsorption properties of the HT were studied by adsorption kinetics. Catalytic experiments with the CZA-HT samples were conducted in a fixed-bed micro reactor. In addition to these experiments, we also conducted control experiments in which mixtures of CZA pellets and hydrotalcite pellets were mixed at a bed level, and mixtures of quartz sand and CZA pellets were conducted at a bed level.
Section snippets
Materials
The copper-based catalyst (CZA) used for methanol synthesis was purchased from Alfa Aesar (Product No. 45776, Lot No. C18W019). The catalyst pellets were ground (with mortar and pestle) to powders with a diameter lower than 0.1 mm before usage.
The hydrotalcite PURAL MG50 (HT) was supplied by Sasol (Product No. 595050) [24]. It was activated by pretreatment at 673 K for 4 h in air.
Preparation of CZA-HT catalysts
CZA-HT catalysts were prepared by physical mixing. Typically, powders of CZA (diameter < 0.1 mm) and hydrotalcite
Thermal stability
Thermal stabilities of CZA and raw hydrotalcite (before activation) analysed by TGA and DTG are shown in Fig. 3. As shown in Fig. 3(a), the CZA only loses 2.4% of its total weight even at a high temperature of 1023 K. The hydrotalcite, by comparison, displays two obvious weight loss stages as temperature is increased, contributing to a total weight loss rate of 38.2%. From the DTG curves in Fig. 3(b), no peak is detected in CZA, but three peaks are distinguished in HT at 475.6, 573.6 and
Conclusion
In this study we assessed the influence of an adsorbent on CO2 conversion to methanol using hydrotalcite as the adsorbent and commercial Cu based catalyst. Catalysts (CZA-HT) containing different contents of hydrotalcite were prepared by physically mixing copper-based catalyst (CZA) and hydrotalcite. Among CZA-HT catalysts, the methanol formation rate based on unit mass of CZA increases along with the HT content in them. All methanol yields acquired with CZA-HT catalysts, though appear
References (51)
- et al.
Integrated synthesis of dimethylether via CO2 hydrogenation
Stud. Surf. Sci. Catal.
(2004) - et al.
Direct CO2-to-DME hydrogenation reaction: new evidences of a superior behaviour of FER-based hybrid systems to obtain high DME yield
J. CO2 Util.
(2017) - et al.
Overcoming the equilibrium barriers of CO2 hydrogenation to methanol via water sorption: a thermodynamic analysis
J. CO2 Util.
(2017) - et al.
Role of ZrO2 in Cu/ZnO/ZrO2 catalysts prepared from the precipitated Cu/Zn/Zr precursors
Catal. Today
(2016) - et al.
Influence of Zr on the performance of Cu/Zn/Al/Zr catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol Peng
J. Catal.
(2013) - et al.
Preparation and characterization of CuZnAl catalysts by citrate gel process
J. Phys. Chem. Solids
(2006) - et al.
Study of CuZn MOx oxides (M = Al, Zr, Ce, CeZr) for the catalytic hydrogenation of CO2into methanol
Comptes Rendus Chim.
(2015) - et al.
Influence of modifier (Mn, La, Ce, Zr and Y) on the performance of Cu/Zn/Al catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol
Appl. Catal. A Gen.
(2013) - et al.
The influence of La doping on the catalytic behavior of Cu/ZrO2 for methanol synthesis from CO2 hydrogenation
J. Mol. Catal. A: Chem.
(2011) - et al.
CO2 hydrogenation to methanol on a YBa2Cu3O7 catalyst
J. Catal.
(2000)
CO2 hydrogenation to methanol over Pd/In2O3: effects of Pd and oxygen vacancy
Appl. Catal. B Environ.
Methanol synthesis using captured CO2 as raw material: techno-economic and environmental assessment
Appl. Energy
Improved methanol yield and selectivity from CO2 hydrogenation using a novel Cu-ZnO-ZrO2 catalyst supported on Mg-Al layered double hydroxide (LDH)
J. CO2 Util.
CO2 hydrogenation to methanol over CuZnGa catalysts prepared using microwave-assisted methods
Catal. Today
Highly efficient Cu-based catalysts via hydrotalcite-like precursors for CO2 hydrogenation to methanol
Catal. Today
Core-shell structured Cu@m-SiO2 and Cu/ZnO@m-SiO2 catalysts for methanol synthesis from CO2 hydrogenation
Catal. Commun.
Methanol synthesis from CO2/H2 using Ga2O3-Pd/silica catalysts: impact of reaction products
Catal. Today
Isotherm model for high-temperature, high-pressure adsorption of CO2 and H2O on K-promoted hydrotalcite
Chem. Eng. J.
Determination of the dispersion and surface oxidation states of supported Cu catalysts
J. Catal.
Catalytic performance of copper supported on zirconia polymorphs for CO hydrogenation
J. Mol. Catal. A: Chem.
Solid-state interactions, adsorption sites and functionality of Cu-ZnO/ZrO2 catalysts in the CO2 hydrogenation to CH3OH
Appl. Catal. A Gen.
Single-step synthesis of dimethyl ether from biomass-derived syngas over CuO-ZnO-MOx(M = Zr, Al, Cr, Ti)/HZSM-5 hybrid catalyst: effects of MOx
Appl. Catal. A Gen.
CO2 hydrogenation to methanol over Cu/ZnO/ZrO2 catalysts prepared via a route of solid-state reaction
Catal. Commun.
Fluorinated Cu/Zn/Al/Zr hydrotalcites derived nanocatalysts for CO2 hydrogenation to methanol
J. CO2 Util.
Activation of Mg-Al hydrotalcite catalysts for aldol condensation reactions
J. Catal.
Cited by (40)
Efficient degradation of tetracycline hydrochloride wastewater by microbubble catalytic ozonation with sludge biochar-loaded layered polymetallic hydroxide
2024, Separation and Purification TechnologyCopper nanoparticles encapsulated in zeolite 13X for highly selective hydrogenation of CO<inf>2</inf> to methanol
2024, Journal of Environmental Chemical EngineeringHighly dispersed Cu-ZnO<inf>x</inf> regulated in zeolite for promoted performance in CO<inf>2</inf> hydrogenation to methanol
2024, Microporous and Mesoporous MaterialsThe critical role of intrinsic physicochemical properties of catalysts for CO<inf>2</inf> hydrogenation to methanol: A state of the art review
2023, Journal of Industrial and Engineering ChemistryDecarbonizing the chemical industry: A systematic review of sociotechnical systems, technological innovations, and policy options
2023, Energy Research and Social ScienceOptimization and understanding of ZnO nanoarray supported Cu-ZnO-Al<inf>2</inf>O<inf>3</inf> catalyst for enhanced CO<inf>2</inf> -methanol conversion at low temperature and pressure
2023, Chemical Engineering JournalCitation Excerpt :Besides, reducing space velocity is beneficial to methanol selectivity as well. Our result is consistent with other prior studies reported in literatures [33–35]. Reaction pressure plays an important role in methanol production as well.