Conversion of Recovered Ammonia and Carbon Dioxide into Urea in the Presence of Catalytically Active Copper Species in Nanospaces of Porous Silica Hollow Spheres

Abstract

The present study firstly reported porous silica hollow spheres as a host material for recovery of ammonia and carbon dioxide and conversion of the compounds into urea. These compounds were effectively introduced into the hollow spheres from an aqueous solution including ammonium and carbonate ions accompanied with catalytically active copper ions from the analyses of diffuse reflectance infrared Fourier transform (DRIFT) spectra and diffusion reflectance ultraviolet–visible and near-infrared (DR UV–vis-NIR) spectra. The ammonium and carbonate ions were converted into urea in the hollow spheres at 323 K under 0.5 MPa of argon atmosphere from the results of the DRIFT spectra. From the results of nitrogen sorption isotherms and X-ray photoelectron spectra (XPS) spectra, the amount of the generated urea depended on the amount of the introduced ammonium ions and the size distribution of the nanospaces in the hollow spheres. Urea was highly generated in the hollow spheres with a high amount of ammonium ions and well-ordered nanospaces from the reactants at high density.

The particle size control of ruthenium-encapsulated hollow silica sphere catalysts for the hydrogenation of carbon dioxide into formic acid

“…However, the particle size growth of the active ruthenium species was not observed on the ruthenium-encapsulated hollow silica spheres, as reported in another work. 40 The results displayed in Fig. 4 and 5 indicated that the activity of the ruthenium-encapsulated hollow silica sphere catalyst was mainly influenced by the dispersion of primary particles of the active metallic ruthenium species, and the particle size of the active species did not significantly change before and after the catalytic reaction.…”

Thermochemical Properties of Synthesized Urea from Recovered Ammonia and Carbon Dioxide in Well-Ordered Nanospaces of Hollow Silica Spheres

“…Otherwise, in the DTA curve of hollow silica spheres prepared with 1-dodecylamine (Figure a), the clear endothermic peak was not observed in the temperature range up to 373 K, while two peaks centered at 440 and 514 K assigned as phase transition and decomposition, respectively, of urea were observed. We previously reported that the yield of urea strongly depended on the size distributions of nanospaces of hollow silica spheres, and the amount of urea in the hollow silica spheres prepared with 1-dodecylamine (229 mg urea g-sample –1 ) with small size and narrow distribution of nanospaces was significantly high compared with those in the hollow spheres prepared with dodecane (76 mg urea g-sample –1 ) and 1-dodecanol (43 mg urea g-sample –1 ) . The results indicate that an appropriate amount of synthesized urea was required to identify thermochemical behaviors of the confined urea by DTA.…”

“…We previously reported that the yield of urea strongly depended on the size distributions of nanospaces of hollow silica spheres, and the amount of urea in the hollow silica spheres prepared with 1dodecylamine (229 mg urea g-sample −1 ) with small size and narrow distribution of nanospaces was significantly high compared with those in the hollow spheres prepared with dodecane (76 mg urea g-sample −1 ) and 1-dodecanol (43 mg urea g-sample −1 ). 13 The results indicate that an appropriate amount of synthesized urea was required to identify thermochemical behaviors of the confined urea by DTA. Otherwise, the peak temperatures in Figure 3c were higher than those of pristine urea.…”

“…5 nm, and ca. 5–10 nm, respectively . Otherwise, from the result of nitrogen sorption measurements in the previous study, only a sharp peak ranging from 1.8 to 4.1 nm centered at 2.9 nm was observed in the distribution of the sample prepared with 1-dodecylamine, while the broad peaks ranging from 4 to 100 nm centered at 3.1 and 3.7 nm were also observed in the distributions of the samples prepared with dodecane and 1-dodecanol accompanied by the sharp peaks ranging from 1.9 to 5.0 nm, respectively .…”

“…Their reduction processes generally proceed under high temperature (<773 K) and pressure (<25 MPa) conditions and thus require high energy consumption for effective conversion of carbon dioxide. Our research group has first demonstrated to produce urea in the nanospaces of porous hollow silica spheres from ammonia and carbon dioxide recovered in the nanospaces from aqueous solution at much lower temperature (323 K) and pressure (0.5 MPa argon atmosphere) in comparison to the commercial synthesis processes (>413 K, >13 MPa) from ammonia and carbon dioxide in gas and liquid phases by means of the Bazarov reaction, as shown in the following equations − 2 NH 3 + CO 2 = NH 4 COONH 2 NH 4 COONH 2 = false( NH 2 false) 2 CO + H 2 normalO where (NH 2 ) 2 CO is urea and NH 4 COONH 2 is ammonium carbamate. In the reaction in the liquid phase, urea was also synthesized from ions such as ammonium and carbonate ions, from which urea was also synthesized in the well-ordered nanospaces of hollow silica spheres reported in our previous study. , The process effectively proceeded only in the well-ordered nanospaces with sizes of ca.…”