This review focuses on important stability issues facing amine-functionalized CO2 adsorbents, including amine-grafted and amine-impregnated silicas, zeolites, metal–organic frameworks and carbons. During the past couple of decades, major advances were achieved in understanding and improving the performance of such materials, particularly in terms of CO2 adsorptive properties such as adsorption capacity, selectivity and kinetics. Nonetheless, to pave the way toward commercialization of adsorption-based CO2 capture technologies, in addition to other attributes, adsorbent materials should be stable over many thousands of adsorption–desorption cycles. Adsorbent stability, which is of utmost importance as it determines adsorbent lifetime and operational costs of CO2 capture, is a multifaceted issue involving thermal, hydrothermal, and chemical stability. Here we discuss the impact of the adsorbent physical and chemical properties, the feed gas composition and characteristics, and the adsorption–desorption operational parameters on the long-term stability of amine-functionalized CO2 adsorbents. We also review important insights associated with the underlying deactivation pathways of the adsorbents upon exposure to high temperature, oxygen, dry CO2, sulfur-containing compounds, nitrogen oxides, oxygen and steam. Finally, specific recommendations are provided to address outstanding stability issues.

Stability of amine-functionalized CO2 adsorbents: a multifaceted puzzle.

Four different types of amine-attached MCM-48 silicas were prepared and investigated for CO(2) separation from N(2). Monomeric and polymeric hindered and unhindered amines were attached to the pore surface of the MCM-48 silica and characterized with respect to their CO(2) sorption properties. The pore structures and amino group content in these modified silicas were investigated by XRD, FT-IR, TGA, N(2) adsorption/desorption at 77 K and CHN/Si analysis, which confirmed that in all cases the amino groups were attached to the pore surface of MCM-48 at 1.5-5.2 mmol/g. The N(2) adsorption/desorption analysis showed a considerable decrease of the pore volume and surface area for the MCM-48 silica containing a polymeric amine (e.g., polyethyleneimine). The CO(2) adsorption rates and capacities of the amine-attached MCM-48 samples were studied employing a sorption microbalance. The results obtained indicated that in addition to the concentration of surface-attached amino groups, specific interactions between CO(2) and the surface amino groups, and the resultant pore structure after amine group attachment have a significant impact on CO(2) adsorption properties of these promising adsorbent materials.

Tailoring pore properties of MCM-48 silica for selective adsorption of CO2

A comparative review between amines and ammonia as sorptive media for post-combustion CO2 capture

Novel Ni-W-Mg mixed oxide catalysts (NiWMgOx) were prepared by homogeneous precipitation and attempted for the methanation of CO2 Adding W remarkably promoted the activity with improved stability, anti-CO-poisoning ability and resistance against coke formation compared to the undoped NiMgOx catalyst The superior reactivity of monodentate formate towards hydrogenation than that of bidentate formate species was identified by DRIFTS analysis and the formation of more active monodentate formate species was indisputably facilitated by W additives, leading to the greatly enhanced catalytic activity H-2-TPR and CO2-TPD characterization showed that doping W increased the number of stable CO2 adsorption sites and helped in anchoring the Ni sites as a result of strengthened Ni-Mg interaction, both of which were responsible for the enhanced CO2 methanation activity and the improved resistance against sintering (C) 2016 Elsevier BV All rights reserved

A novel W-doped Ni-Mg mixed oxide catalyst for CO2 methanation

CO2 adsorption/desorption onto/from tetraethylenepentamine (TEPA) films of 4, 10, and 20 μm thicknesses were studied by in situ attenuated total reflectance (ATR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) techniques under transient conditions. Molar absorption coefficients for adsorbed CO2 were used to determine the CO2 capture capacities and amine efficiencies (CO2/N) of the films in the DRIFTS system. Adsorption of CO2 onto surface and bulk NH2 groups of the 4 μm film produced weakly adsorbed CO2, which can be desorbed at 50 °C by reducing the CO2 partial pressure. These weakly adsorbed CO2 exhibit low ammonium ion intensities and could be in the form of ammonium-carbamate ion pairs and zwitterions. Increasing the film thickness enhanced the surface amine–amine interactions, resulting in strongly adsorbed ion pairs and zwitterions associated with NH and NH2 groups of neighboring amines. These adsorbed species may form an interconnected surface network, which slowed CO2 gas...

https://pubs.acs.org/doi/pdf/10.1021/am5031006

In Situ ATR and DRIFTS Studies of the Nature of Adsorbed CO2 on Tetraethylenepentamine Films

The objective of this research is to develop a new type of CO2 sorbent. The sorbents were synthesized with mesoporous ethane–silica nanotubes (E–SNTs) and tetraethylenepentamine (TEPA). They were characterized by nitrogen adsorption/desorption, thermogravimetric analysis, and infrared spectroscopy. A fixed-bed reactor equipped with an online mass spectrometer was used to test the CO2 capture performances of the sorbents. It was found that 75 °C is the optimal CO2 adsorption temperature for amine-impregnated E–SNT sorbents. The highest CO2 sorption capacities achieved with E–SNTs with 50 wt % TEPA loading (E–SNTs–50%) without and with uses of water vapor are 3.58 and 4.74 mmol/g, respectively, under the conditions of a 10.0% CO2/N2 mixture at 75 °C. Cyclic CO2 adsorption–desorption test results indicate that the new composite sorbents are stable and regenerable.

Tetraethylenepentamine-Modified Silica Nanotubes for Low-Temperature CO2 Capture

The adsorption and desorption of CO2 on MgO/Al2O3 were investigated by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with the method of curve-fitting analysis. The spectroscopic results indicate that there are three chemisorbed surface species formed on the MgO/Al2O3, i.e., free carbonate ion, bridged carbonate, and bidentate carbonate species, which correspond to the peaks at 1675, 1403, and two peaks at 1610 and 1340 cm−1, respectively, when the sample was exposed in CO2 flow at 130 °C. The quantification analysis of the spectra during CO2 adsorption and desorption shows that the formation and desorption rates of all surface species are coverage dependent. Among the three species, the bridged carbonate shows the highest speed of formation and desorption, indicating that this type of species may be beneficial to CO2 capture and release. It should also be noted that the contribution of support Al2O3 to CO2 capture is negligible. This study may help us to understand the interaction between CO2 and metal oxides and thus to give more insights into CO2 capture using solid sorbents.

CO 2 Adsorption and Desorption on MgO/Al 2 O 3 : An In Situ Diffuse Reflection Infrared Fourier Transform Spectroscopy (DRIFTS) Study

The adsorption and desorption of hydrogen on Ir/SiO2 catalyst were studied by using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with curve-fitting analysis. The results indicate that there are three different surface species formed on the catalyst that correspond to the peaks at 1950, 2010, and 2035 cm−1, respectively, when exposed in H2 flow at 130 °C. These surface species display different adsorption and desorption trends. Surface hydride forms after the catalyst is cooled to 80 °C and it disappears after the catalyst is heated to 130 °C again. This study may help us understand the interaction between hydrogen and noble metals and thus give more insights to heterogeneous catalytic mechanism involving hydrogen and hydrogen storage using metal materials.

In situ real-time diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) study of hydrogen adsorption and desorption on Ir/SiO2 catalyst.

The invention relates to a catalyst used for making tetrafluoromethane through gas-phase fluorination and a preparation method thereof, and aims at providing a catalyst used for making tetrafluoromethane through gas-phase fluorination characterized by high activity and high stability and a preparation method thereof in consideration of poor activity and low stability existing in the existing gas-phase fluorination catalyst. The preparation method of the catalyst of the invention is as follows: one or more than one compound of Y, compound of Cr, compound of magnesium, aluminum, indium, gallium, zinc, scandium, strontium, iron, cobalt, nickel and cadmium are measured according to a certain proportion; the precipitator adopts one among ammonia, sodium hydroxide, ammonium carbonate, sodium carbonate and potassium hydroxide, and sediments are obtained by a coprecipitation method, and the precursor of the catalyst is obtained by baking and roasting the sediments then the catalyst is obtained after being treated with anhydrous hydrogen fluoride.

Catalyst for producing tetrafluoromethane with gas-phase fluoridation and production method

The invention provides a gas phase fluorination catalyst and a method for preparing the same. The aim of the invention is to provide a gas phase fluorination catalyst with high activity and stability and a method for preparing the same so as to overcome the defects of poor activity and stability existing in the prior gas phase fluorination catalyst. The catalyst of the invention comprises a carrier and active components, wherein the carrier is a compound of Y, and the active components comprise a compound of chromium and one or more of compounds of magnesium, aluminum, indium, gallium and zinc. The method for preparing the catalyst comprises: according to a certain ratio, the compounds of Y and Cr and one or more of compounds of magnesium, aluminum, indium, gallium and zinc are weighed up, added with water, evenly mixed and added with a precipitator until the precipitation is finished, and the precipitate is separated and the solution washed until the filtrate is neutral, the precipitate is dried, formed and roasted to give the a precursor of the fluorination catalyst, and the precursor of the fluorination catalyst is added with anhydrous HF and treated at a certain temperature to give the gas phase fluorination catalyst.

Gas-phase fluorination catalyst and preparation method thereof

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