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

Abstract

The objective of this work is to develop CuCl@AC adsorbent with high CO capacity and selectivity from CO/N 2 binary gas mixture. A series of CuCl@AC adsorbents were prepared by a solid-state auto dispersion method, and then characterized by N 2 adsorption test, XRD and XPS. CO and N 2 adsorption isotherms on the adsorbents were measured by a volumetric method. The adsorption isotherms and selectivities of CuCl@AC adsorbents for CO/N 2 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/P 0 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/N 2 adsorption selectivities of 1.2CuCl/AC decreased with pressure. Its CO/N 2 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/N 2 mixture separation.

The use of metal–organic frameworks for CO purification

“…These modified activated carbons show greater promise than the aforementioned commercially-available activated carbons for CO purification due to the incorporation of metal sites. First and second-row transition metals as well as post-transition metals salts such as Sn and Al have been LQFRUSRUDWHG LQWR DFWLYDWHG FDUERQV WKURXJK YDULRXV µPHWDO LPSUHJQDWLRQ ¶ PHWKRGV [53][54][55][56][57][58][59][60][61][62] Of the various metals, Cu impregnation is the most prominent. [53][54][55][56][57][58][59][60][61] Overall, as expected, the incorporation of transition metals such as copper increases the materials CO affinity and enhances the potential for selective CO separation, as exemplified in a study with CO/CO2/N2 mixtures.…”

“…While using unsaturated metal sites to selectively adsorb CO molecules has been the most popular route for CO separation using MOFs to date, a number of studies have also been reported for which the goal was to introduce additional preferential adsorption sites through metal impregnation 84,116 and/or ligand functionalization ( Figure 2B). 115,124,125 Metal impregnation, similar to that reported with activated carbon, 59,60 has been performed on highly porous MOFs, e.g. MIL-100 and MIL-101.…”

Optimisation of Cu+ impregnation of MOF-74 to improve CO/N2 and CO/CO2 separations

“…To further improve MOFs' CO uptake, one can use metal impregnation, a method tested on ACs and zeolites. [9][10][11][12][13][14][15][16][17][18] This approach increases selectivity by decreasing the uptake of the undesired light product (e.g. N 2 ) whose affinity with the impregnated metal is low.…”

“…9 Several groups have produced Cu +impregnated zeolites and activated carbons either through the use of a Cu + -containing salt or that of a Cu 2+ -containing salt with subsequent reduction. [9][10][11][12][13][14][15][16][17][18] A similar route has also been conducted on Na-zeolite Y, initially through metal cation exchange with Cu 2+ ions. 19,20 These studies demonstrate that it is favourable to initially perform Cu 2+ impregnation or ionexchange, before reducing to Cu + .…”

“…X-ray photoelectron spectroscopy has been the sole characterisation technique used to conrm the presence of Cu + by the absence of Cu 2+ satellite peaks. 16,21 Yet, this approach can only evaluate the surface, and not the bulk, chemistry of the Cu-impregnated MOFs. Furthermore, the absence of Cu 2+ satellite peaks may be caused by Cu 2+ to Cu 0 over reduction rather than the formation of Cu + .…”