Synthesis methods of dual functional materials

Dual functional materials can be prepared by 1) physically mixing sorbent and catalyst; 2) impregnating catalyst on sorbent; 3) one-pot synthesis of DFMs mixing catalytic and adsorption sites at molecule level.

One-pot synthesis of DFMs

For example, the sol-gel method was used to prepare Ni-CaO DFMs using one-pot synthesis. Details are below (DOI: 10.1126/sciadv.aav5077):

“The CaO-Ni bifunctional sorbent-catalyst was prepared via the well-known Pechini sol-gel method (50, 51) using metal nitrates, citric acid (CA), and ethylene glycol (EG) at a molar ratio of 1:2:2. In a typical synthesis, calculated amounts of Ca(NO₃)₂·4H₂O, Ni(NO₃)₂·6H₂O, and anhydrous CA were dissolved in deionized water, and the as-prepared solution was magnetically stirred at 348 K in an oil bath for 1 hour to form the metal-CA chelates. Then, EG was added to the solution, with the temperature of the resulting solution increased to 363 K. Gelation of the solution occurred through the poly-esterification reaction between EG and metal-CA chelates at 363 K with continuous stirring until the removal of excess solvent. The obtained gel was dried overnight at 373 K in an oven and then calcined at 1073 K for 2 hours. The as-synthesized sorbent-catalysts were labeled as CaO/Ni_x, where x denotes the molar ratio of Ca to Ni in the material. In some cases, the material was fully reduced by H₂ at 1073 K for 3 hours before use (table S2). In addition to the CaO-Ni bifunctional sorbent-catalysts, pure CaO without the loading of Ni was prepared, according to the abovementioned procedures, for comparison.”

One-pot synthesis of DFMs for ICCU-DRM is also reported by S.Molina-Ramírez as blow (https://doi.org/10.1016/j.jcou.2020.101201):

“A novel unsupported metal-alkaline earth metal catalyst was prepared employing an atomic ratio Ni/Ba = 1/1 by coprecipitation with ammonia (30 vol.%) using nickel nitrate and barium nitrate as precursors (Panreac Applichem). 3 % in atomic mass respect to Ni + Ba of colloidal silica (LUDOX HS-40, Aldrich Chemistry, 40 wt.% SiO₂) was added to the mixture. The solution of the precursors and colloidal silica was kept under stirring overnight at 30 °C. Then, it was twice sonicated at room temperature for 5 s before ammonia was dropwise added up to pH = 9. The equipment used consisted of Ultrasonic Processor UIP1000hd (Hielscher) with unchangeable frequency of 20 kHz using a titanium sonotrode. The ultrasonic power intensity was 300 W cm⁻². After ultracentrifugation, the gel was washed with distilled water and dried for 24 h at 80 °C and finally calcinated at 800 °C (ramp of 5 °C min⁻¹) in air for 4 h.”

In addition, Gu et al. (https://doi.org/10.1039/D1TA09967A) also reported the use of one-pot synthesis of SrCe_1−xNi_x DFMs. The reported method is shown below:

“The SrCe_1−xNi_x sorbent catalysts were prepared using a modified Pechini method.^41,42 All the chemical reagents were purchased from Sigma-Aldrich, and a representative preparation process is described below. Initially, a stoichiometric amount of Sr(NO₃)₂ (99.0%), Ce(NO₃)₃·6H₂O (99%) and Ni(NO₃)₂·6H₂O (99.9%) was dissolved in deionized water at 80 °C. Citric acid (99.5%) and ethylene glycol (99.8%) were successively introduced at the molar ration of citric acid : ethylene glycol : cations (Sr²⁺, Ce³⁺ and Ni²⁺) = 3.75 : 2.5 : 1. The solution was kept stirring at 80 °C to form a viscous gel, which was then dried at 180 °C to form a precursor. Finally, the precursor was calcined in a muffle furnace at 900 °C for 3 h. The calcined materials were crushed and double sieved to the size range of 0.1–0.3 mm. To be specific, the materials were named SrCe_1−xNi_x.”

Physically mixing of catalyst and sorbent

In another ICCU-DRM work, sorbent and catalyst were mixed together physically, as indicated below (https://doi.org/10.1021/acs.iecr.9b05783):

“For integrated CO₂ capture and conversion experiment, 1 g of solid materials (i.e., a mixture of 40 wt % Fe₂O₃/Al₂O₃ and CaCO₃ in a mole ratio of 0.80:0.15 (17)) was loaded into the fixed-bed reactor.”

Furthermore, Lv et al. also simply mixed 2 g K-Li₄SiO₄ sorbent and 2 g Ni/Al₂O₃ catalyst for ICCU-DRM (https://doi.org/10.1016/j.seppur.2021.119476).

Impregnation of catalytic sites on sorbent

While in another work, catalytic sites (Ni) and promotor (Ce) were impregnated on adsorbents (CaxZryOz) as described below by the authors (https://doi.org/10.1016/j.apcatb.2020.119734):

“1 g of the as-prepared support was dispersed in 100 mL of absolute ethanol under sonication. For impregnation of Ni, a homogeneous solution was obtained by dissolving the required amount (theoretically reach a 5 wt% Ni loading) of nickel acetylacetonate (≥98 %, Merck) in 100 mL of absolute ethanol (≥99.8 %, Fisher Chemicals) at 60 °C under stirring. For co-impregnation of Ni and Ce, a homogeneous ethanol solution containing the required amount (theoretical Ni or CeO₂ loading: 5 wt%) of nickel acetylacetonate and cerium nitrate hexahydrate (99 % trace metals basis, Aldrich) was prepared. Afterwards, the suspension was added into the homogeneous solution and kept stirring at 60 °C until ethanol was completely evaporated.”