CO Hydrogenation Activity Research Articles

Development of Silicalite-1 encapsulated Cu-ZnO catalysts for methanol synthesis by CO2 hydrogenation

Converting CO2 into fuels and valuable chemicals such as methanol has been gaining significant attention as a favorable solution for reducing greenhouse gas emissions. Although Cu-ZnO-based catalysts are promising candidates for this reaction since methanol is selectively produced at the Cu-ZnO interface, Cu are not stable at elevated temperatures (500–600 K), leading to decrease in the surface areas of Cu and Cu-ZnO interface due to thermal aggregation of Cu. Furthermore, the generation of H2O as a by-product in the CO2 hydrogenation does not only accelerate the aggregation of Cu, but also inhibits an intermediate (formate species) formation for methanol. This paper reports the development of a novel catalyst, annotated as CuPS@S-1 by immobilizing Cu phyllosilicate (CuPS) as the Cu source within hydrophobic zeolite of Silicalite-1 particles (S-1). Cu@S-1 was obtained after the reduction CuPS@S-1 and the size of the Cu particles was approximately 2.4 nm. Cu@S-1 exhibited a higher CO2 hydrogenation activity and methanol selectivity than Cu/S-1 prepared by an impregnation method. To further improve the methanol production activity, ZnO was loaded onto Cu@S-1 to form a Cu-ZnO interface. ZnO/Cu@S-1 was obtained by the impregnation of CuPS@S-1 powder with an ethanol solution containing zinc acetate, followed by calcination and reduction. The obtained catalyst exhibited a better methanol production yield where the space–time yield for methanol based on the Cu weight exceeded 1200 mgmethanol gCu−1h−1.

Mitigating Climate Change through Catalytic Conversions of CO2: A review

In the pursuit of a carbon-neutral economy, CO2 catalytic hydrogenation to methanol emerges as a pivotal technology for mitigating CO2 and addressing the manufacturing needs of future fuels, chemicals, and materials. The development of this technology not only offers solutions to environmental challenges, such as the greenhouse effect, but also facilitates the effective utilization of CO2 resources. The aims of this review is reveal intuitions into the structural and surface properties of heterogeneous catalysts, emphasizing the interface between metal and support. The exploration of these factors delves into their functions in reaction mechanisms, influencing catalytic activity, selectivity, and stability in CO2 hydrogenation to methanol.

Probing the Reactive Intermediates in CO2 Hydrogenation on Ni/Al2O3 Catalysts with Modulation Excitation Spectroscopy

AbstractIn‐situ infrared spectroscopy is one of the most effective methods to study the surface species on solid catalysts. Still, it is sometimes difficult to identify the reactive intermediates because spectator species, the catalyst support, and experimental noise also contribute to the total spectra. In this study, we prepared three archetypical Ni/Al2O3 catalysts that showed significantly different catalytic activity and selectivity for CO2 hydrogenation, depending on the calcination and reduction temperature. After detailed characterization, we used a combination of Modulation Excitation‐Phase Sensitive Detection‐Diffuse Reflectance Infrared Fourier Transform Spectroscopy (ME‐PSD‐DRIFTS) and Steady State Isotopic Kinetic Analysis (SSITKA) to show that bicarbonates and formates are key reactive intermediates. Furthermore, we also observe carbonyls on the catalyst with the most metallic character and highest selectivity towards CH4. These results confirm that the hydrogenation of CO2 occurs in an associative and consecutive reaction pathway that is highly structure‐sensitive. In this way, we also demonstrate how the simultaneous collection of spectroscopic and kinetic data during modulated or transient experiments is a powerful tool for investigating solid catalysts under realistic operation conditions.

Visualization of the Active Sites of Zinc-Chromium Oxides and the CO/H2 Activation Mechanism in Direct Syngas Conversion.

Despite wide studies demonstrating the versatility of the metal oxide-zeolite (OXZEO) catalyst concept to tackle the selectivity challenge in syngas chemistry, the active sites of metal oxides and the mechanism of CO/H2 activation remain to be elucidated. Herein, we demonstrate experimentally the role of Cr in zinc-chromium oxides and unveil visually, for the first time, the active sites for CO activation employing scanning transmission electron microscopy-electron energy loss spectroscopy using the volumetric density of surface carbon species as a descriptor. The ZnCr2O4 spinel surface with atomic ZnOx overlayer is the most active site for C-O bond dissociation, particularly at the narrow ZnCr2O4(110) facets constrained between the (311) and (111) facets, followed by the Cr-doped wurtzite ZnO surface. In comparison, the surfaces of ZnCr2O4 with aggregated ZnOx overlayers, pure ZnO, and the stoichiometric ZnCr2O4 exhibit a significantly lower activity. In situ synchrotron-based vacuum ultraviolet photoionization mass spectrometric study on different temperature programmed surface reactions with isotopes of C18O, 13CO, and D2 validates direct CO dissociation over ZnCrn oxides in CO, forming CH2 and further to hydrocarbons if H2 is present and CH2CO intermediates in syngas. The activity of CO dissociation and hydrogenation over ZnCrn oxides correlates well with the syngas-to-light-olefins activity of ZnCrn-SAPO-18 composite catalysts as a function of the Cr/Zn ratio.

Multiscale modelling of CO2 hydrogenation of TiO2-supported Ni8 clusters: on the influence of anatase and rutile polymorphs

The selection of TiO2 phase, whether anatase or rutile, for supporting small Ni clusters significantly influences the activity and selectivity in CO2 hydrogenation to methane.

Alkali-promoted indium oxide as a highly active and selective catalyst for photo-thermal CO2 hydrogenation

Cs-promoted In2O3 has demonstrated excellent catalytic activity and selectivity in photo-thermal CO2 hydrogenation. Mechanistic studies suggest that non-thermal effects prevail, particularly at low reaction temperatures and high light intensities.

Support effect on Ni-based mono- and bimetallic catalysts in CO2 hydrogenation.

Aiming at a comprehensive understanding of support effects on Ni-based bimetallic catalyst for CO2 hydrogenation, spectroscopy (DRIFTS) with CO as a probe molecule and temperature-programmed techniques were used to investigate the impact of different supports (MgO, CeO2, ZrO2) on Ni- and Ni,Fe catalysts. Kinetic parameters revealed that the higher selectivity to methanation for Ni and Ni,Fe supported on the reducible oxides (CeO2, ZrO2) is due to the inhibition of reverse water-gas shift reaction (RWGS) by hydrogen. A promoting effect of Fe on Ni was only observed on MgO-supported catalysts. In situ DRIFTS with CO adsorption showed different electronic properties of Ni sites with partially reduced oxide (i.e. ZrO2 and CeO2). H2-TPR and CO2-TPD confirmed the significant role of metal-support interaction (MSI) in CeO2-supported catalysts for CO2 activation. The MSI between Ni/Ni,Fe and reducible supports are crucial for catalytic performance, ultimately leading to the higher activity and stability in CO2 hydrogenation.

Theoretical insights into the generation and reactivity of hydride on the ZnO(101̄0) surface.

ZnO is an important catalytic material for CO/CO2 hydrogenation. In this work, the pristine ZnO(101̄0) and the surfaces with Zn-O dimer vacancies (ZnO(101̄0)-(Zn-O)DiV) and oxygen vacancies are calculated. We find that the hydride (H-) species can be generated via heterolytic H2 dissociation on these surfaces, and that ZnO(101̄0)-(Zn-O)DiV only needs to overcome the energy barrier of ∼0.10 eV. This is because the ZnO system has flexible orbitals for electron storage and release and the low-coordinated Zn3c atoms at the defect sites can form stable Zn-H- covalent bonds with high symmetry. Flexible Zn orbitals also impart the unique feature of activating multiple electrophilic adsorbates simultaneously as excess electrons exist. Moreover, we show that the covalent Zn-H- species can regulate the catalytic activity and selectivity for CO2 hydrogenation by preferentially producing *HCOO intermediates at Zn-O dimer vacancies. These results may help in the design of efficient Zn-based hydrogenation catalysts.

Mn-promoted MoS2 catalysts for CO2 hydrogenation: enhanced methanol selectivity due to MoS2/MnOx interfaces.

Considering the alarming scenario of climate change, CO2 hydrogenation to methanol is considered a key process for phasing out fossil fuels by means of CO2 utilization. In this context, MoS2 catalysts have recently shown to be promising catalysts for this reaction, especially in the presence of abundant basal-plane sulfur vacancies and due to synergistic mechanisms with other phases. In this work, Mn-promoted MoS2 prepared by a hydrothermal method presents considerable selectivity for CO2 hydrogenation to methanol in comparison with pure MoS2 and other promoters such as K and Co. Interestingly, if CO is used as a carbon source for the reaction, methanol production is remarkably lower, which suggests the absence of a CO intermediate during CO2 hydrogenation to methanol. After optimization of synthesis parameters, a methanol selectivity of 64% is achieved at a CO2 conversion of 2.8% under 180 °C. According to material characterization by X-ray Diffraction and X-ray Absorption, the Mn promoter is present mainly in the form of MnO and MnCO3 phases, with the latter undergoing convertion to MnO upon H2 pretreatment. However, following exposure to reaction conditions, X-ray photoelectron spectroscopy suggests that higher oxidation states of Mn may be present at the surface, suggesting that the improved catalytic activity for CO2 hydrogenation to methanol arises from a synergy between MoS2 and MnOx at the catalyst surface.

Reactivity of surface oxygen vacancy sites and frustrated Lewis acid-base pairs of In2O3 catalysts in CO2 hydrogenation.

The effects of oxygen vacancy (VO) formation energy and surface frustrated Lewis acid-base pairs (SFLPs) on the CO2 hydrogenation activity of In2O3 catalysts were studied using density functional theory calculations. The VO formation energy of 2.8-3.3 eV was found to favor HCOO formation, whereas the presence of SFLPs is conducive to CO formation.

Synergistic effect of K and Zn on Fe-based catalysts for efficient CO2 hydrogenation.

Excessive emission of CO2 into the atmosphere has severely impacted the global ecological environment. Converting CO2 into valuable chemicals and fuels is of great significance for sustainable development. However, low activity and undesirable selectivity often result from the inherent inertness of CO2. Herein, K- or/and Zn-modified Fe-based catalysts were prepared by an incipient-wetness impregnation method for CO2 hydrogenation via a cascade reaction. The results indicate that K species exist as K2O while Zn species exist as ZnFe2O4. In the CO2 hydrogenation pathway, K2O facilitates the adsorption of CO2 and restrains the adsorption of H2, accelerating the transformation of CO2 into C2-C4 olefins rather than paraffins while Zn species promote the dispersion of Fe species, leading to improved activity. Synergistically, a K- and Zn-modified Fe-based catalyst (2Zn-10K-Fe/Al) shows excellent catalytic CO2 hydrogenation activity, achieving a CO2 conversion of 77% which is 1.8 times that (42%) of the unmodified Fe-based catalyst (Fe/Al). Our catalyst also shows a significantly promoted selectivity to C2-C4 olefins of 17% in comparison with the Fe/Al catalyst (0%). It is envisioned that such a binary effect of elements might contribute to the low-cost and industrial production of Fe-based catalysts for selective CO2 conversion.

Enhanced Methanol Synthesis over Self-Limited ZnOx Overlayers on Cu Nanoparticles Formed via Gas-Phase Migration Route.

Supported metal catalysts are widely used for chemical conversion, in which construction of high density metal-oxide or oxide-metal interface is an important means to improve their reaction performance. Here, Cu@ZnOx encapsulation structure has been in situ constructed through gas-phase migration of Zn species from ZnO particles onto surface of Cu nanoparticles under CO2 hydrogenation atmosphere at 450 °C. The gas-phase deposition of Zn species onto the Cu surface and growth of ZnOx overlayer is self-limited under the high temperature and redox gas (CO2 /H2 ) conditions. Accordingly, high density ZnOx -Cu interface sites can be effectively tailored to have an enhanced activity in CO2 hydrogenation to methanol. This work reveals a new route for the construction of active oxide-metal interface and classic strong metal-support interaction state through gas-phase migration of support species induced by high temperature redox reaction atmosphere.

Enhanced Methanol Synthesis over Self‐Limited ZnOx Overlayers on Cu Nanoparticles Formed via Gas‐Phase Migration Route

AbstractSupported metal catalysts are widely used for chemical conversion, in which construction of high density metal‐oxide or oxide‐metal interface is an important means to improve their reaction performance. Here, Cu@ZnOx encapsulation structure has been in situ constructed through gas‐phase migration of Zn species from ZnO particles onto surface of Cu nanoparticles under CO2 hydrogenation atmosphere at 450 °C. The gas‐phase deposition of Zn species onto the Cu surface and growth of ZnOx overlayer is self‐limited under the high temperature and redox gas (CO2/H2) conditions. Accordingly, high density ZnOx‐Cu interface sites can be effectively tailored to have an enhanced activity in CO2 hydrogenation to methanol. This work reveals a new route for the construction of active oxide‐metal interface and classic strong metal‐support interaction state through gas‐phase migration of support species induced by high temperature redox reaction atmosphere.

Tuning CO adsorption states via enhanced metal-support interaction for boosting CO2 methanation activity of Ru/rutile-TiO2

Understanding the correlation between metal–support interactions (MSIs) and the adsorption states of reaction intermediates is critical for developing heterogeneous catalysts. To modulate MSIs and CO adsorption states, various Ru/Ti1-xCrxO2 catalysts were prepared by Cr3+ cation doping and used for CO2 methanation compared to the rutile TiO2-supported Ru catalyst (Ru/r-TiO2). The activity followed the order: Ru/Ti0.95Cr0.05O2 > Ru/Ti0.97Cr0.03O2 > Ru/Ti0.87Cr0.13O2 ≫ Ru/r-TiO2. The best Ru/Ti0.95Cr0.05O2 catalyst possessed CO2 turnover frequency (TOF) value at 200 °C 10.2 times higher than that on the Ru/r-TiO2. Cr3+ doping in the lattice of r-TiO2 support led to the Ru/Ti0.95Cr0.05O2 with higher dispersion of Ru and enhanced MSIs. A linear-CO*-II intermediate formed on the Ru/Ti0.95Cr0.05O2 with higher C-O vibrational frequency (2003 cm−1) than the linear-CO*-I at 1972 cm−1 on the Ru/r-TiO2, and the blue-shifted CO possessed higher activity for CO hydrogenation to CH4. The higher activity of the linear-CO* were accounting for the much higher TOF value of the Ru/Ti0.95Cr0.05O2. The strength of MSIs was proved to be highly correlated with CO adsorpton states including the balance of the strength of Ru-C and C-O bonds, which were found to be a crucial factor for the activity of supported Ru-based catalysts for CO hydrogenation.

K-guided selective regulation mechanism for CO2 hydrogenation over Ni/CeO2 catalyst

Regulating the selectivity between CO and CH4 during CO2 hydrogenation is a challenging research topic. Previous research has indicated that potassium (K) modification can adjust the product selectivity by regulating the adsorption strength of formate/CO* intermediates. Going beyond the regulation mechanism described above, this study proposes a K-guided selectivity control method based on the regulation of key intermediates HCO*/H3CO* for Ni catalysts supported on reducible carrier CeO2. By incorporating K, the CO selectivity of CO2 hydrogenation shifts from around 25.4% for Ni/CeO2 to approximately 93.8% for Ni/CeO2-K. This can be attributed to K modification causes electron aggregation in the bonding regions of HCO* and H3CO* intermediates, thus enhancing their adsorption strength. Consequently, the reaction pathway from HCO*/H3CO* to CH4 is limited, favoring the decomposition of formates to CO products. Moreover, the addition of K leads to a moderate decrease in CO2 conversion from 55.2% to 48.6%, which still surpasses values reported in most other studies. This reduction is associated with a decline in reducible Ni species and oxygen vacancy concentration in Ni/CeO2-K. As a result, the adsorption capacity for CO2 and H2 reduces, ultimately reducing CO2 hydrogenation activity.

First-principles study of CO2 hydrogenation on Cd-doped ZrO2: Insights into the heterolytic dissociation of H2.

Cd-doped ZrO2 catalyst has been found to have high selectivity and activity for CO2 hydrogenation to methanol. In this work, density functional theory calculations were carried out to investigate the microscopic mechanism of the reaction. The results show that Cd doping effectively promotes the generation of oxygen vacancies, which significantly activate the CO2 with stable adsorption configurations. Compared with CO2, gaseous H2 adsorption is more difficult, and it is mainly dissociated and adsorbed on the surface as [HCd-HO]* or [HZr-HO]* compact ion pairs, with [HCd-HO]* having the lower energy barrier. The reaction pathways of CO2 to methanol has been investigated, revealing the formate path as the dominated pathway via HCOO* to H2COO* and to H3CO*. The hydrogen anions, HCd* and HZr*, significantly reduce the energy barriers of the reaction.

Effect of sodium promoters on Ni/Al2O3 catalyst for CO2 hydrogenation: The carbon fixation as carbon nanofiber and reverse-water gas reactions

Reducing CO2 emissions has become a critical priority in addressing the environmental impact of carbon dioxide. Technologies for CO2 fixation primarily involve carbon capture storage and utilization (CCSU) and chemical conversion, typically pursued along independent tracks. In our research, we have focused on developing a catalytic reaction for CO2 hydrogenation that integrates the benefits of both CCSU and chemical conversion. The use of sodium-promoted Ni/Al2O3 catalyst (NiNax/Al2O3) in the CO2 hydrogenation process exhibits a synergistic effect, leading to the simultaneous production of CO, CH4, and carbon nanofibers (CNFs). Notably, the conversion of CO2 into CNFs represents a novel approach for carbon fixation, in addition to the formation of CO and CH4. Importantly, the formation of CNFs on the NiNax/Al2O3 catalyst does not compromise its catalytic activity for CO2 hydrogenation to CO and CH4, which is a noteworthy finding. This bifunctional catalyst has the potential to offer significant advantages, including high CO production and the generation of valuable carbon materials. The CNFs are predominantly formed at the interfacial sites between NiNax and Al2O3. The formation process involves the reaction between H2 bound to Ni and adsorbed CO2, leading to the formation of hydrogen carbonate species, which subsequently give rise to CNFs. The reduction of CO2 to CNFs is facilitated by the transfer of electrons from Al3+ species to the interfacial sites between NiNax and Al2O3.

Revealing the effect of metal-support interactions at the Ni/In2O3(111) interface on the selective CO2 hydrogenation

In2O3-supported Ni catalysts exhibit remarkable catalytic activity and selectivity in CO2 hydrogenation to methanol, but the underlying mechanisms and metal-oxide interactions during the reaction remain elusive. Herein, we investigate the Ni-In2O3 interaction by physical vapor deposition of Ni onto well-defined In2O3(111) thin films. In-situ near ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) was employed to probe the CO2 hydrogenation processes on these Ni/In2O3(111) model systems. Our results reveal that the small Ni clusters supported on the In2O3(111) surface at low Ni coverages exhibit cationic states. The chemical bonding and associated electron transfer at the Ni/In2O3(111) interface play crucial roles in the activation of H2 and CO2. Importantly, reaction intermediates (CO3*, OH, and HCOO*) are readily formed and desorbed under CO2 hydrogenation conditions. Our study highlights the significance of metal-support interactions on the selectivity of CO2 hydrogenation. These findings provide valuable insights into the rational design of advanced In2O3-based catalysts for CO2 hydrogenation.

Interfacial synergistic catalysis of Cun single-cluster catalysts anchored on α-Al2O3(0001) for promoting hydrogenation of CO2 to methanol

The size-selected copper single-cluster catalysts(SCCs) play a crucial role in catalyzing of CO2 hydrogenation. However, nature of size effect and hydrogenation mechanism is still unclear. Here, Density functional theory(DFT) calculations were performed to investigate activation and reaction mechanism of CO2 hydrogenation to methanol over copper single-clusters catalyst anchored on α-Al2O3(0001). Our results show that Cun(n = 1–9)/Al2O3 catalysts significantly promote activation of CO2 in a bent configuration due to the synergistic interaction associated with Cun-Al2O3(0001) interfacial site. Bader charge analysis suggested electron transfer occurring from Cun-Al2O3(0001) interface to CO2, leading to negatively charged CO2. We find descriptors of deviation of CO2 bonds length and bonds angle, d-band center of Cun(n = 1–9) cluster that can well descript for determining activation degree of CO2. Especially, the Cu5/α-Al2O3(0001) has the best activity for CO2 hydrogenation among them. Furthermore, reaction mechanism of CO2 hydrogenation at Cu5/Al2O3 interface have been explored. Methanol synthesis takes formate route and direct CO bond cleavage route competitive with rate-dominant step of HCOO* and HO* hydrogenation, respectively. While CO-hydrogenation produced by RWGS route is not feasible because of high activation barrier of formed CO intermediate(1.95 eV). This study will provide insight into designing and application of ultrahigh-performance Cu-based single-cluster catalysts for CO2 hydrogenation.

Interface mediated CO2 hydrogenation on inverse supported ZrO2/Ni(1 1 1) nanocluster catalyst

To tune the activity and selectivity of CO2 hydrogenation, inverse supported Zr9O18/Ni(111) catalysts are designed based on ab initio molecular dynamics simulation and density functional theory calculation under the consideration of the number of interfacial O and Zr atoms as well as the interaction between O and Zr atoms. For the most stable catalyst with coordinatively unsaturated interface Zr sites, charge transfer from surface to oxide has been found. The Ni(111) surface is pre-covered by H atoms and the interface Zr sites can activate CO2 to a large extent, and their interaction results in the spontaneous formation of surface formate. Further hydrogenation of surface formate leads to the selective formation of methanol with an apparent Gibbs free energy barrier of 0.62 eV, lower than that of methane formation (1.09 eV). On the contrary to metallic nickel and supported nickel catalysts, the most favoured methanol formation route [HCOO → CHO → CH2O → CH3O → CH3OH] does not involve CO as intermediate, revealing the mediated interface effect.