Hydrotalcite Precursors Research Articles

Designing highly active hydrotalcite-derived NiAl catalysts for methane cracking to H2

Designing nickel-based methane cracking catalysts with excellent catalytic activity and surveying their transition during the catalytic process with varied reaction condition have been challenge. In this paper, NiAl catalysts were prepared by reduced hydrotalcite precursor for efficient catalytic methane cracking to produce hydrogen. The catalysts were characterized by XRD, N2 physisorption, XPS, SEM, TEM, Raman and TGA. The effects of preparation method, Ni/Al ratio and reaction temperature on methane cracking performance were revealed and the transformation for the Ni particles during the reaction process was analyzed. The results indicated that the catalyst performance of hydrotalcite-derived NiAl catalysts is superior to Ni/Al2O3 catalysts prepared by the conventional impregnation method, which maybe due to the better Ni dispersion and uniform average particle size distribution with around 12.7 nm compared with the agglomeration of the Ni/Al2O3 particles for up to 53.2 nm. The catalyst with a Ni/Al molar ratio of 3 exhibited the optimal catalytic activity with a stability for 75 min at nearly 90 % hydrogen yield at 700 °C. The reaction temperature also suggested a positive correlation between the hydrogen yield and the reaction temperature from 600 °C to 800 °C. Moreover, based on the investigation of the catalysts during the reaction transition state, Ni particles sintered rapidly from 10.2 nm to 31.2 nm at the beginning reaction time with the high hydrogen yield and then tended to be stable, which may be correlated well with the degree of graphitization of the deposited carbon. This paper provides a valuable design for efficient methane cracking catalysts.

Active-site engineering of a frustrated-Lewis-pair Au-loaded Zn-Al catalyst for the highly stable synthesis of glycerol carbonate from co-utilisation of CO2 and glycerol

Solid frustrated-Lewis-pair catalysts, based on Zn-Al composite oxide modified loaded with Au (Aux/ZnAl-CHT), were prepared by calcination of hydrotalcite precursors and tested for the direct synthesis of glycerol carbonate using CO2 as the carbon source. An Au5/ZnAl-CHT catalyst shows the highest catalytic performance with the glycerol carbonate yield of 19.5 % and the selectivity of 50.5 % at 170 °C and 4.0 MPa CO2, while maintaining good thermal stability and excellent regeneration ability. A series of characterization results and density functional theory (DFT) calculations indicated the introduction of Au leads to more frustrated-Lewis-pairs in Zn-Al composite oxide (ZnAl-CHT), which improve the adsorption and activation of CO2. Meanwhile, FTIR analysis indicates that glycerol is activated by Zn2+ for the formation of zinc glycerolate intermediates. The above dual synergistic activation processes effectively enhance the catalytic performance. And the reaction pathway is proposed for the synthesis of glycerol carbonate from CO2 and glycerol.

The influence of Mg/Al molar ratio on the performance of CuMgAl-x catalysts for CO2 hydrogenation to methanol.

The CuMgAl-x catalysts derived from hydrotalcite precursors with different Mg/Al molar ratios were synthesized and applied to CO2 hydrogenation to methanol reaction. In this study, the effects of Mg/Al molar ratio on the structure and surface properties of CuMgAl-x catalysts were investigated by XRD, N2 adsorption-desorption, SEM, TEM, H2-TPR, CO2-TPD, XPS, and in situ DRIFTS characterization methods. The results showed that an appropriate Mg/Al molar ratio can enhance the Cu-MgO interaction, increasing the basic sites and obtaining suitable acid sites. The dispersion of active Cu on the CuMgAl-x catalysts can be improved by strong Cu-MgO interaction, which enhances the adsorption capacity of CO2 and makes H2 activation easier, accelerates the conversion of intermediate species CO3 * and HCO3 *to HCOO*, and facilitates further conversion to CH3O* and CH3OH. The strong interaction between Cu and MgO was conducive to the formation of Cu+, which can inhibit the desorption of CO in the reverse water gas shift reaction. The CuMgAl-3 catalyst showed the highest CO2 Conversion rate (14.3%), methanol selectivity (94.5%), and STY of methanol (419.3g⋅kgcat. -1⋅h-1) at 240°C and 2.5MPa. The results obtained in this paper can provide a new idea for the design of high-performance catalysts for CO2 hydrogenation to methanol.

Ce enhanced RuNi alloy multi-metal synergic hydrotalcite oxide derived catalyst for high performance CO2 methanation

Ni-based methanation catalysts have problems such as low temperature activity and easy sintering. The high cost of supported Ru-based methanation catalysts limits their application in industrialization. In this work, a hydrotalcite precursor Ru-Ni-Ce-Y catalyst was prepared by co-precipitation method, and the hydrotalcite oxide catalyst was prepared by high temperature calcination. The hydrotalcite oxide catalyst was prepared by optimizing the ratio of Ni element and the amount of precious metal and rare earth metal. Compared with the traditional supported catalyst, the activity of Ru1Ni80Ce4Y20 was significantly improved. It is confirmed from the experimental results that the medium basic sites, oxygen vacancies and the synergistic effect between RuNi alloy and Ce are the reasons for the high performance of Ru1Ni80Ce4Y20. It provides a thought for the design of highly active, stable and low cost methanation catalysts in industrial methanation production.

Green technology for carbon dioxide utilization: Vermiculite based hydrotalcite for methane dry reforming

In this paper, the abundant metal ions in the vermiculite-modified waste stream were utilized to prepare vermiculite-based hydrotalcite precursors, and hydrotalcite-like bimetallic catalysts were synthesized by the co-precipitation method and used in the methane dry reforming reaction. The experimental results showed that the Ni-Co/VMT-LDO catalyst showed good activity with 84% CH4 conversion and 87% CO2 conversion at 750 °C and 18000 mL/(g·h). The catalyst was characterized by XRD, SEM, BET, H2-TPR, TEM and TG. TEM tests before and after the reaction showed that the addition of Co decreased the average particle size of Ni. Meanwhile, thermogravimetric tests of the spent catalysts revealed that the weight loss of the bimetallic catalysts was significantly smaller than that of the monometallic catalysts, in which the Ni-Co/VMT-LDO showed better anti-carbon accumulation performance than the other two catalysts. This study not only solves the environmental problems caused by vermiculite modification, but also enhances the economic utilization of vermiculite. Vermiculite-based hydrotalcite-loaded bimetallic catalysts have been shown to be effective catalysts for dry reforming of methane.

Fabrication of NiTi-MMO supported on in-situ generated TiO2 for dioctyl phthalate hydrogenation: A strategy for improving the utilization efficiency of Ni

In this work, a NiTi-MMO/TiO2-R catalyst was prepared by in-situ generation of a TiO2 support during hydrothermal synthesis of the hydrotalcite precursor for NiTi-MMO. The formation of NiTi-MMO can reduce the size of metallic Ni particles, which can significantly improve the catalyst's activity, and the in-situ generated TiO2 support can enhance the dispersion of NiTi-MMO and the utilization efficiency of the active nickel species. The NiTi-MMO/TiO2-R catalyst showed high activity for the hydrogenation of dioctyl phthalate to dioctyl-1,2-cyclohexanedicarboxylate. The catalyst also exhibited good stability, maintaining the yield over 90 % after 6 cycles. Characterization results showed that a strong metal-support interaction was formed between the in-situ generated TiO2 support and the metallic Ni particles produced by the reduction of NiTi-MMO. The strong metal-support interactions formed between metallic Ni particles and the in-situ generated TiO2 played a crucial role in stabilizing the nickel species and preventing their aggregation, resulting in superior catalytic performance.

Water and Cu+ Synergy in Selective CO2 Hydrogenation to Methanol over Cu-MgO-Al2O3 Catalysts.

The CO2 hydrogenation reaction to produce methanol holds great significance as it contributes to achieving a CO2-neutral economy. Previous research identified isolated Cu+ species doping the oxide surface of a Cu-MgO-Al2O3-mixed oxide derived from a hydrotalcite precursor as the active site in CO2 hydrogenation, stabilizing monodentate formate species as a crucial intermediate in methanol synthesis. In this work, we present a molecular-level understanding of how surface water and hydroxyl groups play a crucial role in facilitating spontaneous CO2 activation at Cu+ sites and the formation of monodentate formate species. Computational evidence has been experimentally validated by comparing the catalytic performance of the Cu-MgO-Al2O3 catalyst with hydroxyl groups against that of its hydrophobic counterpart, where hydroxyl groups are blocked using an esterification method. Our work highlights the synergistic effect between doped Cu+ ions and adjacent hydroxyl groups, both of which serve as key parameters in regulating methanol production via CO2 hydrogenation. By elucidating the specific roles of these components, we contribute to advancing our understanding of the underlying mechanisms and provide valuable insights for optimizing methanol synthesis processes.

Ni–Fe nanoparticles prepared using hydrotalcite precursors enhance the photocatalytic performance of CO2 methanation

A series of Fe-modified bimetallic hydrotalcite-like photocatalysts are prepared through co-precipitation containing amounts of M2+(NO3)2·6H2O (M2+ = Mg, Ni) and M3+(NO3)3·9H2O (M3+ = Al, Fe) with a fixed Ni content and a monometallic 25Ni/Al2O3 catalyst for comparison purpose. The main objective of this experimental work is to study the replacement of Al with Fe in the photocatalyst on the CO2 methanation performance under three different reaction conditions (dark, ultraviolet and visible illumination). Thus, the use of Fe as a promoter has been studied for improving the light adsorption capability of photocatalysts and the reducibility of active metals. However, the results showed that modification by Fe acting as active metal and as support modification, is less effective than modification by Al. Therefore, the effects of both the basicity and photothermal activation by plasmonic nanoparticles under ultraviolet and visible photocatalytic conditions improve the methane production compared to the reaction under dark conditions.

Preparation of a green and highly active vermiculite-derived hydrotalcite and its application in methane dry reforming

By utilizing the abundant metal ions in modified vermiculite waste solution and doping with Ni ions, a Ni-based precursor like hydrotalcite was directly synthesized using co-precipitation method for methane dry reforming reaction. Performance testing conducted at 750 °C showed that the catalyst exhibited excellent activity, with a CH4 conversion rate of 85.76 % and a CO2 conversion rate of 84.42 %. This outstanding performance can be attributed to the uniform distribution and appropriate particle size of the catalyst prepared from the hydrotalcite precursor, as well as the strong metal-support interaction between metal carriers due to the orderly distribution of nickel.

Upgrading bio-butanol in the presence of copper-hydrotalcite derived mixed oxides: From batch to continuous flow catalytic process highly selective to butyl butyrate

The conversion of bio-alcohols to chemicals and fuels can play a determinant role in the transition towards bio-economy. Different hydrotalcite derived Cu/Mg/Al mixed oxides, having a Cu atomic content in the range 1.0–7.6 %, have been employed for the first time in batch and continuous flow reactors for the conversion of n-BuOH. The catalytic performances resulted strongly tunable, being influenced by the composition of the catalytic systems and by the type of adopted reactor. The catalysts with lower Cu content resulted active both in the Guerbet condensation to 2-ethyl-1-hexanol (2EH) and in the dehydrogenative coupling (DHC) of the substrate to butyl butyrate (BB) ester, while the catalyst with the highest Cu content showed very high selectivity towards BB formation. The batch reaction evidenced a progressive deactivation of the catalytic systems with the reconstruction of the hydrotalcite precursor. On the other hand, the study in flow reactor revealed good activity and excellent stability of the catalytic system Cu7.6, a selectivity to BB > 98 mol% being maintained after 216 h of time-on-stream.

Engineering the Quaternary Hydrotalcite-Derived Ce-Promoted Ni-Based Catalysts for Enhanced Low-Temperature CO2 Hydrogenation into Methane.

Ce-promoted NiMgAl mixed-oxide (NiCex-C, x = 0, 1, 5, 10) catalysts were prepared from the quaternary hydrotalcite precursors for CO2 hydrogenation to methane. By engineering the Ce contents, NiCe5-C showed its prior catalytic performance in low-temperature CO2 hydrogenation, being about three times higher than that of the Ce-free NiCe0-C catalyst (turnover frequency of NiCe5-C and NiCe0-C: 11.9 h-1 vs. 3.9 h-1 @ 225 °C). With extensive characterization, it was found that Ce dopants promoted the reduction of NiO by adjusting the interaction between Ni and Mg(Ce)AlOx support. The highest ratio of surface Ni0/(Ni2+ + Ni0) was obtained over NiCe5-C. Meanwhile, the surface basicity was tailored with Ce dopants. The strongest medium-strength basicity and highest capacity of CO2 adsorption was achieved on NiCe5-C with 5 wt.% Ce content. The TOF tests indicated a good correlation with medium-strength basicity over the NiCex-C samples. The results showed that the high medium-strength and Ce-promoted surface Ni0 species endows the enhanced low-temperature catalytic performance in CO2 hydrogenation to methane.

Enhanced activity and coke resistivity of NiCoFe nanoalloy catalyst in CO2 reforming of methane

NiCo nanoalloy catalysts were prepared from hydrotalcite precursors and used in CO2 reforming of methane (DRM) under atmospheric and 2 MPa pressure in a fixed-bed reactor at 700-850 °C. The Ni6Co1 catalyst with a molar ratio of Ni/Co to 6 showed the highest stability and activity in DRM under atmospheric pressure. This was due to the homogeneous dispersion of nanoalloy particles (∼14 nm) on the MgAl(O) support, which had a strong metal-support interaction. Nonetheless, a slow and continuous deactivation was spotted under 2 MPa pressure due to the coke deposition. Further modification of Ni6Co1 with optimum amount of Fe (in Ni6Co0.5Fe0.5) formed ternary NiCoFe nanoalloy with improved metal-support interaction and reduced alloy size (∼10 nm). The presence of Fe significantly improved the coke resistance capability and provided high stability under 2 MPa pressure.

A study of CO2 hydrogenation over Ni-MgAlOx catalysts derived from hydrotalcite precursors

Ni/Mg/Al mixed oxides have been prepared by decomposing corresponding layered double hydroxides of the hydrotalcite family. XRD, FTIR and UV–vis–NIR analyses show that prepared materials are constituted by a rock-salt type Mg1−xNixO solid solution with Al3+ in tetrahedral interstices of the cube close packing of oxide anions. When activated at sufficiently high temperature, they convert into optimal size supported Ni metal catalysts which show very active and selective for CO2 methanation. Catalytic data show that these materials are more active at low temperature than Ni/γ-Al2O3 catalysts, with a comparable enhanced activity with respect to Ni/La2O3-Al2O3 ones. A role of basic oxides as activating components can be envisaged and related to the strength of the adsorption of CO2 on the “support” likely forming surface (bi)carbonates as active species. Activation energies and reactions orders have been calculated by flow reactor studies in differential reactor conditions. IR spectroscopy data show that carbon dioxide adsorbs on the reduced catalyst in the form of hydroxycarbonates, that convert at higher temperature in carbonates and strongly adsorbed linear and bridging carbonyl species on metallic nickel. The formation of surface CHx species is also evident.

In-situ constructed ultrathin hydrotalcite derivative supported PtIn catalyst for isobutane direct dehydrogenation

The stable and ultrathin hydrotalcite nanosheets with thickness of ca. 1.0 nm have been built on the surface of Al2O3 by sharing Al element and using layer growth inhibitor formamide. Based on the topological transformation characteristics of hydrotalcite and the structural memory effect of calcined product, the supported PtIn bimetallic catalyst was achieved by stepwise incipient wetness impregnation method followed by calcination and reduction, and evaluated in isobutane direct dehydrogenation (IDH) to isobutene. The derived ultrathin bimetallic catalyst possesses excellent IDH activity under extreme conditions, in which the isobutane conversion and isobutene selectivity can remain above 63% and 92% respectively, and the turnover frequency is as high as 13.45 s−1. The excellent activity can be attributed to the formation of ultrathin hydrotalcite precursor, which can greatly enhance the specific surface area, interaction among metal components, surface acidity of weak- and medium-acid sites and surface In3+/In0 ratio, and further effectively inhibit carbon deposition and improve dispersion and stability of active Pt species in the corresponding derivative.

CuCeOx/CuO Catalyst Derived from the Layered Double Hydroxide Precursor: Catalytic Performance in NO Reduction with CO in the Presence of Water and Oxygen.

Valencies of metal species and lattice defects, such as oxygen vacancies, play a pivotal role in metal oxide-catalyzed reactions. Herein, we report a promising synthetic strategy for preparing CuO-supported CuCeOx catalysts (CuCeOx/CuO) by calcination of a hydrotalcite precursor [Cu6Ce2(OH)16]CO3·nH2O. The structural and chemical properties of catalysts were characterized by XRD, ICP-AES, TEM, TPR, NH3-TPD, XPS, Raman spectroscopy, and N2 adsorption, which revealed that the thermal pretreatment in an oxidative atmosphere caused segregation and reconstitution processes of the precursor, resulting in a mesoporous catalyst consisting of well-dispersed CuO-supported CuCeOx clusters of 1.8-3.2 nm in size with a high population of oxygen vacancies. The as-prepared catalyst shows excellent catalytic performance in the reduction of NO by CO in the absence as well as in the presence of water and oxygen. This behavior is attributed to its high oxygen defect concentration facilitating the interplay of the redox equilibria between Cu2+ and reduced copper species (Cu+/Cu0) and (Ce4+/Ce3+). The high surface population of oxygen vacancies and in situ-generated metallic copper species have been evidenced by Raman spectroscopy and X-ray photoelectron spectroscopy. The layered double hydroxide-derived CuCeOx/CuO also showed good water tolerance and long-term stability. In situ infrared spectroscopy investigations indicated that adsorbed hyponitrite species are the main reaction intermediates of the NO conversion as also corroborated by theoretical simulations.

Plasma-Catalytic CO2 Reforming of Toluene over Hydrotalcite-Derived NiFe/(Mg, Al)O x Catalysts.

The removal of tar and CO2 in syngas from biomass gasification is crucial for the upgrading and utilization of syngas. CO2 reforming of tar (CRT) is a potential solution which simultaneously converts the undesirable tar and CO2 to syngas. In this study, a hybrid dielectric barrier discharge (DBD) plasma-catalytic system was developed for the CO2 reforming of toluene, a model tar compound, at a low temperature (∼200 °C) and ambient pressure. Periclase-phase (Mg, Al)O x nanosheet-supported NiFe alloy catalysts with various Ni/Fe ratios were synthesized from ultrathin Ni-Fe-Mg-Al hydrotalcite precursors and employed in the plasma-catalytic CRT reaction. The result demonstrated that the plasma-catalytic system is promising in promoting the low-temperature CRT reaction by generating synergy between DBD plasma and the catalyst. Among the various catalysts, Ni4Fe1-R exhibited superior activity and stability because of its highest specific surface area, which not only provided sufficient active sites for the adsorption of reactants and intermediates but also enhanced the electric field in the plasma. Furthermore, the stronger lattice distortion of Ni4Fe1-R provided more isolated O2- for CO2 adsorption, and having the most intensive interaction between Ni and Fe in Ni4Fe1-R restrained the catalyst deactivation induced by the segregation of Fe from the alloy to form FeO x . Finally, in situ Fourier transform infrared spectroscopy combined with comprehensive catalyst characterization was used to elucidate the reaction mechanism of the plasma-catalytic CRT reaction and gain new insights into the plasma-catalyst interfacial effect.

Cu‐Co/ZnAl2O4 Catalysts for CO Conversion to Higher Alcohols Synthesized from Co‐Precipitated Hydrotalcite Precursors

AbstractThe role of Cu:Co composition in bi‐metallic Cu‐Co/ZnAl2O4 catalysts on higher alcohol synthesis (HAS) was investigated at H2:CO = 4. The addition of Cu strongly facilitated Co reduction upon catalyst activation and suppressed coke deposition during HAS. Formation of predominantly hydrocarbons and higher alcohols was observed on the bi‐metallic catalysts. Co/ZnAl2O4 produced mainly CH4 and Cu/ZnAl2O4 mainly CH3OH, while at Cu:Co = 0.6 the best ethanol selectivity of 4.5 % was reached. The microstructure of the spent catalysts confirmed a close interaction of Cu and Co.

Precursor engineering of hydrotalcite-derived redox sorbents for reversible and stable thermochemical oxygen storage

Chemical looping processes based on multiple-step reduction and oxidation of metal oxides hold great promise for a variety of energy applications, such as CO2 capture and conversion, gas separation, energy storage, and redox catalytic processes. Copper-based mixed oxides are one of the most promising candidate materials with a high oxygen storage capacity. However, the structural deterioration and sintering at high temperatures is one key scientific challenge. Herein, we report a precursor engineering approach to prepare durable copper-based redox sorbents for use in thermochemical looping processes for combustion and gas purification. Calcination of the CuMgAl hydrotalcite precursors formed mixed metal oxides consisting of CuO nanoparticles dispersed in the Mg-Al oxide support which inhibited the formation of copper aluminates during redox cycling. The copper-based redox sorbents demonstrated enhanced reaction rates, stable O2 storage capacity over 500 redox cycles at 900 °C, and efficient gas purification over a broad temperature range. We expect that our materials design strategy has broad implications on synthesis and engineering of mixed metal oxides for a range of thermochemical processes and redox catalytic applications.

Hydrotalcite-Derived Copper-Based Oxygen Carrier Materials for Efficient Chemical-Looping Combustion of Solid Fuels with CO2 Capture.

Chemical-looping combustion (CLC) is a promising technology that utilizes metal oxides as oxygen carriers for the combustion of fossil fuels to CO2 and H2O, with CO2 readily sequestrated after the condensation of steam. Thermally stable and reactive metal oxides are desirable as oxygen carrier materials for the CLC processes. Here, we report the performance of Cu-based mixed oxides derived from hydrotalcite (also known as layered double hydroxides) precursors as oxygen carriers for the combustion of solid fuels. Two types of CLC processes were demonstrated, including chemical looping oxygen uncoupling (CLOU) and in situ gasification (iG-CLC) in the presence of steam. The Cu-based oxygen carriers showed high performance for the combustion of two solid fuels (a lignite and a bituminous coal), maintaining high thermal stability, fast reaction kinetics, and reversible oxygen release and storage over multiple redox cycles. Slight deactivation and sintering of the oxygen carrier occurred after redox cycles at an very high operation temperature of 985 °C. We expect that our material design strategy will inspire the development of better oxygen carrier materials for a variety of chemical looping processes for the clean conversion of fossil fuels with efficient CO2 capture.

Insights on Guerbet Reaction: Production of Biobutanol From Bioethanol Over a Mg-Al Spinel Catalyst.

The production of biobutanol from bioethanol by the Guerbet reaction is an alternative pathway to renewable sources. The commercial viability of this green route requires improvements in the process development. This study experimentally examines the influence of operating conditions on the performance of a Mg–Al spinel catalyst prepared from hydrotalcite precursors. This catalyst demonstrates an exceptional performance in the Guerbet reaction with a promising activity/butanol selectivity balance, excellent long-term stability, and very-low-carbon footprint (CO2 generation as by-products is minimal). This study showcases a systematic strategy to optimize the reaction parameters in the Guerbet reaction for biobutanol production using an advanced spinel catalyst. Upon carefully adjusting temperature, pressure, space velocity, and reactants co-feeding, very promising conversion (35%) and butanol selectivity values (48%) were obtained.