High CO Adsorption Capacity Research Articles

Fine-Tuning of Pt Dispersion on Al2O3 and Understanding the Nature of Active Pt Sites for Efficient CO and NH3 Oxidation Reactions.

Fine-tuning the dispersion of active metal species on widely used supports is a research hotspot in the catalysis community, which is vital for achieving a balance between the atomic utilization efficiency and the intrinsic activity of active sites. In this work, using bayerite Al(OH)3 as support directly or after precalcination at 200 or 550 °C, Pt/Al2O3 catalysts with distinct Pt dispersions from single atoms to clusters (ca. 2 nm) were prepared and evaluated for CO and NH3 removal. Richer surface hydroxyl groups on AlOx(OH)y support were proved to better facilitate the dispersion of Pt. However, Pt/Al2O3 with relatively lower Pt dispersion could exhibit better activity in CO/NH3 oxidation reactions. Further reaction mechanism study revealed that the Pt sites on Pt/Al2O3 with lower Pt dispersion could be activated to Pt0 species much easier under the CO oxidation condition, on which a higher CO adsorption capacity and more efficient O2 activation were achieved simultaneously. Compared to Pt single atoms, PtOx clusters could also better activate NH3 into -NH2 and -HNO species. The higher CO adsorption capacity and the more efficient NH3/O2 activation ability on Pt/Al2O3 with relatively lower Pt dispersion well explained its higher CO/NH3 oxidation activity. This study emphasizes the importance of avoiding a singular pursuit of single-atom catalyst synthesis and instead focusing on achieving the most effective Pt species on Al2O3 support for targeted reactions. This approach avoids unnecessary limitations and enables a more practical and efficient strategy for Pt catalyst fabrication in emission control applications.

Competitive mechanism for capturing heavy metal contamination by iron-based porous composite particles for soil remediation

The heavy metal ions of the Cd and As generally co-exist in soil to threaten crop growth and human health. How to simultaneously reduce the activity of the soil Cd and As is still a big challenge because of their entirely opposite chemical properties. A multi-porous humic acid-ferric oxide (HAs-FeOx) composites composed of the core of FeOx polyhedral nanoparticles and the HAs cover are synthesized by hydrothermal method and coprecipitation for the co-immobilization of the soil Cd and As. A high co-adsorption capacity of 178.5 and 91.0 mg/g is obtained for the heavy metal contamination Cd and As in water and the corresponding available states decrease by 98% and 83% in soil based on the developed HAs-FeOx composite, respectively. First-principles calculations and adsorption kinetics analysis demonstrate that active sites of the HAs-FeOx composites for co-capturing heavy metal contamination presents competitive effect, resulting in the reduction activity of the soil Cd through chemisorption process and the reduction activity of the soil As that involves both chemisorption and physisorption process. This work provides an efficient method based on the interfacial-surface engineering to co-immobilize the heavy metal contaminations for soil remediation.

Facile Approach to the Fabrication of Highly Selective CuCl-Impregnated θ-Al2O3 Adsorbent for Enhanced CO Performance.

We have developed a facile and sustainable method to produce a novel θ-Al2O3-supported CuCl adsorbent through impregnation methods using CuCl2 as the precursor. In an easy two-step process, θ-Al2O3 was impregnated with a known concentration of CuCl2 solutions, and the precursor was calcined to prepare CuCl oversupport. The developed novel θ-Al2O3-supported CuCl adsorbent was compared with an adsorbent prepared through the conventional method using CuCl salt. The adsorbents were characterized via X-ray diffraction (XRD), thermal gravimetric analysis (TGA) and temperature-programmed reduction (H2-TPR). Overall, the adsorbent indicates a high CO adsorption capacity, high CO/CO2 and CO/N2 selectivity, and remarkable reusability performance. This process is operated at ambient temperature, which minimizes operation costs in CO separation processes. In addition, these results indicate that the systematic evaluation of alumina-supported CuCl adsorbent can provide significant insight for designing a realistic PSA process for selective CO separation processes.

A highly stable CuO-derived adsorbent with dual Cu(I) sites for selective CO adsorption

Cu(I)-based adsorbents with high stability and adsorption capacity enable effective carbon monoxide separation. Starting from CuO nanoparticles, we synthesized a CO adsorbent with Cu2O and CuCl on the surface by a two-step synthesis route. The first step was a fast thermal reduction under 5 vol% flow of H2 at 673 K. CuCl was then introduced by a room temperature liquid-phase reaction between surface metallic copper and CuCl2. X-ray diffraction was used to investigate the stability of the dual-active site adsorbent under atmospheric air. Compared to single Cu(I) site counterparts, the dual-active site adsorbent has a superior adsorption capacity and selectivity for CO, making itself a promising candidate for CO-CO2 mixture separation. Site energy distribution was used to describe the heterogeneity of the adsorbent surface based on equilibrium adsorption isotherm models. Each synthesis step resulted in the formation of sites at both high and low ends of the site energy spectrum. Adsorption kinetics of CO and CO2 to the adsorbent was also investigated by fitting kinetics results to various adsorption kinetic models. We found that adventitious metallic copper reaction with air forms new active Cu2O sites. Further reaction with ambient air formed a protective layer of copper oxide and carbonate on the surface. These surface moieties enhanced adsorbent stability under atmospheric air for up to 10 days while retaining the adsorption capacity once activated. The oxygen-resistant layer can be easily removed by heating under a vacuum. This study provides a path for the design and synthesis of Cu(I)-based adsorbents with high CO adsorption capacity and stability.

Creating Cu(I)-decorated defective UiO-66(Zr) framework with high CO adsorption capacity and selectivity

• Defective UiO-66 was rapidly fabricated by continuous-flow microwave synthesis. • The surface area and pore width of UiO-66 (Zr) were improved by defects. • The most defective 25Cu(I)@UiO-66 had the highest CO uptake capacity of 2.44 mmol/g. • Defective Cu(I)@UiO exhibited improved CO selectivity. • Cu(I)@UiO-66(Zr) showed good renewability and oxygen-resistant ability. Developing a highly effective material for CO storage and separation is a challenge. In this study, we first used microwave-assisted continuous-flow synthesis to create defective UiO-66(Zr) frameworks with improved surface area and pore structures, which is highly efficient for large-scale production. The defect concentration of UiO-66(Zr) was rapidly and effectively controlled within a short reaction time of 10 min. Different amounts of Cu 2+ were loaded onto defective UiO-66 samples, followed by reducing Cu 2+ to Cu + to obtain Cu(I)@UiO-66 adsorbents (Cu(I)@UiO). X-ray diffraction (XRD), N 2 -adsorption, FT-IR, SEM, TEM, thermogravimetric analysis (TGA), and XPS analyses were used to characterize the physicochemical properties of the prepared adsorbent materials. Gas adsorption experiments revealed that Cu(I)-decorated defective UiO-66 exhibited high CO adsorption capacity due to the π complexation between Cu + and CO. The CO adsorbing amount and CO selectivity onto the Cu(I)@UiO-66 samples were improved by adjusting the defect concentration and Cu(I) load on the UiO-66 host. The breakthrough experiment confirms that this defective Cu(I)@UiO adsorbent can efficiently separate CO/N 2 mixture under dynamic mixture flow conditions. Furthermore, after several cyclic adsorption–desorption experiments, the defective Cu(I)@UiO-66 is highly regenerable and has a good oxygen-resistant ability. The study describes a simple and scalable method for producing π-complexation adsorbent for CO adsorption.

Chelating Cu-N within Cu+-incorporated MIL-101 (Cr)-NH2 framework for enhanced CO adsorption and CO/CO2 selectivity

The development of π-complexation adsorbents with Cu(I) having high CO adsorption capacity, high selectivity, large working capacity, and good stability is still very challenging up to now. In this work, π-complexation adsorbent with Cu+ was fabricated by reducing Cu2+ to Cu+ within amino-functionalized MIL-101 (Cr) framework by employing formate (HCOO-) at low temperature. The obtained results indicated that the Cu+ yield was strongly influenced by the chelation of Cu(II) species into amino groups (NH2) of MIL-101 (Cr)-NH2. The produced CuCl@MIL-101(Cr)-NH2 (CuCl@MCrN) was then applied for CO and CO2 adsorption at various conditions. The results revealed that the formed Cu+ species within MIL-101 (Cr)-NH2 not only increased CO adsorption via CO π-complexation but also reduced CO2 adsorption on the adsorbent through interaction with NH2 groups, resulting in a significant increase of CO/CO2 selectivity onto CuCl@MCrN adsorbent. At 25 °C and 100 kPa, the prepared CuCl@MCrN adsorbent with 30% Cu(I) exhibited the maximum CO uptake amount and CO/CO2 selectivity of ~ 2.52 mmol g−1 and ~ 97, respectively, exceeding those of the benchmark Cu+-based π-complexation adsorbents. The breakthrough experiment indicates that this Cu(I)@MIL-101(Cr)-NH2 adsorbent can efficiently separate CO/CO2mixture under dynamic mixture flow conditions. Moreover, the oxygen-resistant ability of the adsorbent tested under atmospheric humidity conditions demonstrated that CuCl@MCrN adsorbent had good stability.

Study on preparation of CuCl/REY adsorbent with high CO adsorption and selectivity

In this paper, rare earth elements are used to modify Y zeolite, and CuCl-loaded rare earth Y zeolite adsorbents (CuCl/REY) were prepared by solid monolayer dispersion method. The adsorption performance of CuCl/REY on CO was studied, and the adsorbents were characterized via nitrogen adsorption/desorption at 77 K, X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM). We also characterize the state of Cu through temperature-programmed reduction using hydrogen (H2-TPR). The results show that rare earth can slightly increase the pore size, while maintaining the stability of the zeolite framework structure. Also, it can inhibit the production of copper oxide (CuO) to increase the CO capacity, and reduce the adsorption of N2 to increase the CO/N2 selectivity. Under the condition of 298 K and 1 bar, CuCl/REY showed a high CO adsorption capacity of 2.64 mmol/g, and the selectivity of CO/N2 reached 53, which was nearly double the performance of the adsorbent prepared with NaY zeolite.

Facile co-removal of As(V) and Sb(V) from aqueous solution using Fe-Cu binary oxides: Structural modification and self-driven force field of copper oxides

Currently, the environmental and ecological damage caused by As(V) and Sb(V) co-contamination has attracted widespread attention worldwide. Due to the similar intrinsic structure configuration and electrostatic repulsion of As(V) and Sb(V), the long-standing issue of their low co-removal capacity remains unresolved. In this study, novel Fe-Cu (FC) binary materials with varied Fe/Cu proportions were synthesized via a simple co-precipitation method to co-eliminate aquatic As(V) and Sb(V). A 2/1 ratio of Fe/Cu was determined to be a suitable proportion with a higher co-adsorption capacity, specifically 70.9 mg·g−1 for As(V) and 94.3 mg·g−1 for Sb(V). Detailed morphological and structural analyses indicated that the FC material gradually changed from microscale aggregates to nanoscale spheres with increasing Cu content, accompanied by an increasing crystalline degree and higher surface area. Additionally, the transformation of amorphous ferrihydrite (FO) into FeO(OH) was suppressed by Fe-Cu complexion during the co-adsorption process, in which ferrihydrite (FO) had more adsorption sites than FeO(OH). In addition, the addition of Cu promoted the pHpzc of FC materials from the acidic range into the neutral or alkaline range. The increased potential difference of FC materials accelerated the As(V) and Sb(V) diffusion rate and effectively offset native electrostatic repulsion, which exhibited a considerable effect than the adsorption sites. Through detailed kinetic data analysis, it was determined that the proportion of the diffusion layer thickness around Sb(V) was suppressed to the As(V) level, and the adsorption kinetics of the two species were both promoted by the self-driven force field. All the results indicated that the co-adsorption capacity depended on the coupling contribution of Fe and Cu, where Fe oxide acted as the major adsorption potential and Cu provided a self-driven force for As(V) and Sb(V) diffusion. This study may provide a novel prospective for homogeneous metal ion co-removal.

Double-solvent-assisted synthesis of bimetallic CuFe-incorporated MIL-101(Cr) for improved CO-adsorption performance and oxygen-resistant stability

In this study, a bimetallic CuFe-incorporated MIL-101(Cr) adsorbent was developed with enhanced CO-adsorption capacity and oxygen resistance. Different compositions of bimetallic Cu(II)–Fe(II) were incorporated into the MIL-101(Cr) framework with ultrahigh porosity by the double-solvent (DS) method, followed by facile reduction at a low temperature of 250 °C. By employing formate (HCOO−), Cu(II) was selectively reduced to Cu(I) at 250 °C. Moreover, the presence of the reducing agent, Fe(II), enhanced the reduction of Cu(II) in the adsorbent. The obtained results indicated that the synergistic effect of utilizing Fe(II) and employing the DS method significantly enhanced the dispersion of the formed Cu(I) in the support. The DS-assisted CuFe (4 mmol g−1 of CuCl and 1.0 mmol g−1 FeCl2)-incorporated MIL-100(Fe) adsorbent exhibited a high CO-adsorption capacity of ca. 3.24 mmol g−1 and CO/N2 selectivity of 428 at 25 °C and 100 kPa, which were superior to those of the counterpart that was prepared by the wetness impregnation method. Additionally, the CO-adsorption capacity of the prepared CuFe-incorporated MIL-100(Fe) was still 90–65% after it was exposed to atmospheric humidity for 15–30 days, thereby demonstrating its superior oxygen-resistant stability compared to those of the benchmark π-complexation adsorbents containing Cu(I).

High CO Adsorption Performance of CuCl-Modified Diatomites by Using the Novel Method “Atomic Implantation”

An atomic implantation method was used to modify diatomite with CuCl. The CuCl/diatomite samples were characterized by different techniques, including FTIR, XRD, BET, SEM-TEM, EDX, and CO-TPR. Characterization results revealed the formation of CuCl particles of 50–60 nm highly dispersed on diatomite surface. CO adsorption measurements showed that 2CuCl/diatomite exhibits the highest CO adsorption capacity among all CuCl-modified samples with diatomite. Its CO adsorption capacity of 2.96 mmol/g at 30°C is 10 times higher than that of unmodified diatomite (0.29 mmol/g). The CO adsorption on CuCl-modified diatomites was found to fit well with the Langmuir–Freundlich model.

Metal oxide/CeO2 nanocomposites derived from Ce-benzene tricarboxylate (Ce-BTC) adsorbing with metal acetylacetonate complexes for catalytic oxidation of carbon monoxide.

Herein, a series of metal oxide/CeO2 (M/CeO2) nanocomposites derived from Ce-benzene tricarboxylate (Ce-BTC) adsorbing with different metal acetylacetonate complexes were prepared for CO oxidation under four different CO gas atmospheres. It was demonstrated that Cu/CeO2 exhibited the highest catalytic activity and stability in CO oxidation. Remarkably, both O2 selectivity and CO selectivity to CO2 are 100% in most of the investigated conditions. Several analytical tools such as N2 adsorption–desorption and powder X-ray diffraction, were employed to characterize the prepared catalysts. In addition, the excellent catalytic performance of Cu/CeO2 in CO oxidation was revealed by H2 temperature-program reduction experiment, X-ray photoelectron spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The result showed that high oxygen vacancy and high CO adsorption capacity (Cu+–CO) caused by the electron exchanges of Cu2+/Cu+ and Ce3+/Ce4+ pairs (Ce4+ + Cu+ ⇆ Ce3+ + Cu2+) are two key factors contributing to the high oxidation performance of Cu/CeO2 catalyst.

A novel approach to prepare Cu(I)Zn@MIL-100(Fe) adsorbent with high CO adsorption capacity, CO/CO2 selectivity and stability via controlled host–guest redox reaction

The development of a CO-selective adsorbent with large CO adsorption capacity, high CO/CO2 selectivity, and good stability is an industrial challenge. In this study, a novel Cu(I)-incorporated MIL-100(Fe) adsorbent for CO/CO2 separation is prepared using a host–guest redox strategy by exploiting the co-addition of Zn(II) and Cu(II). The addition of Zn(II) resulted in a higher Cu(I) yield of the adsorbent due to the facilitated regeneration of Fe(II), which was utilized for the reduction of Cu(II). Remarkably, the CO/CO2 selectivity (104) of Cu(I)Zn@MIL-100(Fe)-10 was considerably higher than that of the benchmark Cu(I)-incorporated adsorbents. Increasing the Zn(II) concentration in Cu(I)Zn@MIL-100(Fe)-10 improved the oxygen resistance. Density functional theory calculations support our hypothesis that the above improvements are derived from stronger σ-bonding between Cu(I) and CO and the facilitation of Fe(II) regeneration by the addition of Zn(II). This study opens a new perspective for developing efficient CO-selective π-complexation adsorbents with high CO/CO2 selectivity and superior oxygen resistance.

Cost-effective and eco-friendly synthesis of MIL-101(Cr) from waste hexavalent chromium and its application for carbon monoxide separation

Conventionally, MIL-101(Cr) has been directly prepared from analytically pure trivalent chromium (Cr(III)) with the assistance of hydrofluoric acid (HF). Here, we report a novel approach of HF-free synthesis of MIL-101(Cr) using a waste Cr source. A wastewater model containing a high concentration of hexavalent Cr (Cr(VI)) was first reduced by sulfite to obtain Cr(III) at room temperature and subsequently, the resulting solution was directly used as a precursor for MIL-101(Cr) synthesis without HF. The synthesized MIL-101(Cr) had surface area of 2850m2/g and pore volume of 1.54cm3/g which are comparable to the one conventionally prepared with analytically pure Cr(III). The MIL-101(Cr) after Cu(I) loading became CO-selective π complexation adsorbents, showing much higher CO adsorption capacity (2.82mmol/g) than CO2 (0.85mmol/g) and N2 (0.08mmol/g).

CO Adsorption Performance of CuCl/Activated Carbon by Simultaneous Reduction–Dispersion of Mixed Cu(II) Salts

CO is a toxic gas discharged as a byproduct in tail gases from different industrial flue gases, which needs to be taken care of urgently. In this study, a CuCl/AC adsorbent was made by a facile route of physically mixing CuCl2 and Cu(HCOO)2 powder with activated carbon (AC), followed by heating at 533 K under vacuum. The samples were characterized by X-ray powder diffraction (XRD), inductively coupled plasma optical emission spectrometry (ICP-OES), N2 adsorption/desorption, and scanning electron microscopy (SEM). It was shown that Cu(II) can be completely reduced to Cu(I), and the monolayer dispersion threshold of CuCl on AC support is 4 mmol·g−1 AC. The adsorption isotherms of CO, CO2, CH4, and N2 on CuCl/AC adsorbents were measured by the volumetric method, and the CO/CO2, CO/CH4, and CO/N2 selectivities of the adsorbents were predicted using ideal adsorbed solution theory (IAST). The obtained adsorbent displayed a high CO adsorption capacity, high CO/N2, CO/CH4, and CO/CO2 selectivities, excellent ad/desorption cycle performance, rapid adsorption rate, and appropriate isosteric heat of adsorption, which made it a promising adsorbent for CO separation and purification.

High CO adsorption capacity, and CO selectivity to CO2, N2, H2, and CH4 of CuCl/bayerite adsorbent

Abstract We synthesized nanoporous CO-selective adsorbent composed of CuCl supported on bayerite. Before supporting the CuCl, the bayerite chemical was calcined at 623 K to increase the surface area to 469 m2 g−1. The CuCl was highly dispersed on the activated bayerite via a thermal monolayer dispersion process. The highest CO adsorption capacity was achieved at an optimal temperature of 573 K and CuCl content of 30 wt%. Thus synthesized adsorbent exhibited a high CO adsorption capacity of 48.5 cm3 g−1 at 293 K, but a very low CO2 adsorption capacity (2.89 cm3 g−1), resulting in CO/CO2 separation factor of 16.8. When the CuCl content increased to 36 wt%, the adsorbent exhibited much higher separation factor (35.5), although the CO adsorption capacity was somewhat smaller (41.6 cm3 g−1). The CO adsorption capacity and CO/CO2 selectivity of this adsorbent are larger than those of our previous CuCl/boehmite adsorbent showing CO adsorption of 34 cm3 g−1 and a CO/CO2 separation factor of 12.4. The present adsorbent also shows very high selectivity for CO over H2, N2, and CH4. Therefore, this adsorbent is expected to show excellent CO separation performance for various industrial processes such as steam-reforming and steel-making which involve CO, CO2, H2, N2, and CH4.

Selective adsorption of CO on CuCl/Y adsorbent prepared using CuCl2 as precursor: Equilibrium and thermodynamics

Zeolite Y supported CuCl (CuCl/Y) has been prepared with CuCl2 as precursor by a monolayer dispersion method, followed by activation with CO. The samples are investigated for CO adsorption and characterized by inductively coupled plasma optical emission spectrometry, X-ray diffraction, N2 adsorption/desorption and X-ray photoelectron spectroscopy. The characterization results reveal that CuCl2 supported on zeolite Y can be completely reduced to CuCl after activation at 663K in CO, and the monolayer dispersion capacity of CuCl on zeolite Y support is 5mmol/g zeolite Y. The resulting adsorbent displays high CO adsorption capacity, high CO/N2, CO/CH4 and CO/CO2 adsorption selectivities, and excellent reversibility and regenerability. The adsorption equilibrium isotherms of CO on the adsorbents at temperatures up to 333K can be well fitted by both the Langmuir and Sips models, and the integral thermodynamic data of Gibbs’ energy change (ΔG), entropy change (ΔS) and enthalpy change (ΔH) are calculated from the fitted Langmuir adsorption equations. The negative ΔG and ΔH values indicate that the adsorption process of CO on CuCl/Y adsorbent is spontaneous and exothermic. The negative ΔS value indicates that the adsorbed CO molecules on the adsorbent are in an ordered arrangement.

Selective CO adsorbent CuCl/AC prepared using CuCl2 as a precursor by a facile method

CuCl/AC adsorbent with high CO adsorption capacity and selectivity was prepared using CuCl2 as precursor by monolayer dispersion method.

Preparation of CuCl@AC with high CO adsorption capacity and selectivity from CO/N2 binary mixture

The objective of this work is to develop CuCl@AC adsorbent with high CO capacity and selectivity from CO/N2 binary gas mixture. A series of CuCl@AC adsorbents were prepared by a solid-state auto dispersion method, and then characterized by N2 adsorption test, XRD and XPS. CO and N2 adsorption isotherms on the adsorbents were measured by a volumetric method. The adsorption isotherms and selectivities of CuCl@AC adsorbents for CO/N2 binary mixture were estimated on the basis of ideal adsorbed solution theory (IAST). Results showed that (a) CO uptakes of CuCl@AC increased with CuCl loading in the loading range of 0–1.2 g/g. The maximal CO adsorption capacity of the CuCl@AC with CuCl loading of 1.2 g/g reached 38 cc/g at the P/P0 of 0.40, around 8 times of that over the original AC; (b) calcination time for the preparation of Cu(I)@AC had significantly impact on CO adsorption of the adsorbents due to valence change of Cu species on carbon surfaces. XPS analysis indicated that when the calcination time was optimized to be 1 h at 350 °C under argon, the prepared Cu(I)@AC had the highest percentage of Cu+ species on its surfaces, and consequently it had the highest CO capacity among the adsorbents since adsorptive species responsible for CO adsorption is Cu+; (c) The IAST-predicted CO/N2 adsorption selectivities of 1.2CuCl/AC decreased with pressure. Its CO/N2 selectivity was up to 100–450 at low pressure range of 0–10 kPa, and it remained in the range of 50–100 at higher pressure range of 20–100 kPa. The high adsorption capacity and selectivity of Cu(I)@AC adsorbents made it a promising adsorbent for CO/N2 mixture separation.

A supported Cu(I)@MIL-100(Fe) adsorbent with high CO adsorption capacity and CO/N2 selectivity

A supported Cu(I)@MIL-100(Fe) adsorbent was developed for the separation of CO/N2 binary gas mixture. The Cu(I)@MIL-100(Fe) was prepared by the wetness impregnation of the divalent copper salts on MIL-100(Fe), followed by the reduction of Cu2+→Cu+ under vacuum at elevated temperature. The samples were characterized by N2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The adsorption isotherms of CO and N2 on Cu(I)@MIL-100(Fe) were measured by the volumetric method, and the CO/N2 adsorption selectivities of the samples were calculated based on ideal adsorbed solution theory (IAST). The results showed that (a) the Cu(I)@MIL-100(Fe) adsorbent achieved a superior CO adsorption capacity of 2.78mmol/g at 298K and 100kPa, 7 times of that on parent MIL-100(Fe), and the adsorption behavior was well described by the dual-site Langmuir–Freundlich model; (b) the CO/N2 adsorption selectivity of Cu(I)@MIL-100(Fe) was up to 169 at 100kPa, being 112 times of that of parent MIL-100(Fe); (c) the significant enhancement of CO uptake and CO/N2 selectivity can be mainly attributed to the selective π-complexation between CO and Cu(I) on Cu(I)@MIL-100(Fe).

A comparative study on the catalytic properties of high Ni-loading Ni/SiO2 and low Ni-loading Ni-Ce/SiO2 for CO methanation

Two Ni-based catalysts of 13%Ni/SiO2 (13Ni/Si) and 7%Ni-2%Ce/SiO2 (7Ni-2Ce/Si, by weight) were prepared by the incipient-wetness impregnation method and characterized with N2-sorption, XRD, H2-TPR, FT-IR, TEM, H2-TPD and CO-TPD techniques. It was shown that addition of Ce promoter generated an interaction among NiO, CeO2 and SiO2, which changed chemical environment of Ni-O-Si bond, enhanced the dispersion and reduction of NiO, and increased the active surface area. In particular, a new type of moderately strong CO adsorption sites was formed on the surface of the 7Ni-2Ce/Si catalyst. As a result, the low Ni-loading 7Ni-2Ce/Si catalyst exhibited higher CO adsorption capacity and CO methanation catalytic activity than the high Ni-loading 13Ni/Si. Under the reaction conditions of 1% CO (volume fraction in H2 atmosphere), GHSV of 7000 h−1 and atmospheric pressure, the temperature for complete conversion of CO over the 7Ni-2Ce/Si catalyst was 230°C, being 30°C lower than that found over the high Ni loading 13Ni/Si catalyst.