Experimental and theoretical insights into binary Zn-SBA-15/KI catalysts for the selective coupling of CO₂and epoxides into cyclic carbonates under mild conditions

Abstract

Abstract:The combination of metal modified SBA-15 catalyst with potassium iodide was developed as heterogeneous dual catalysts for chemical fixation of CO2 to cyclic carbonates. It was observed that the binary Zn-SBA-15/KI catalysts were the most efficient among various metal modified SBA-15/KI catalysts and showed excellent synergetic effect in promoting the reaction under mild conditions. Moreover, the effects of reaction parameters on cycloaddition of CO2 with propylene oxide (PO) to propylene carbonate (PC) were optimized. Under the optimal conditions determined, Zn-SBA-15/KI catalytic system was also versatile to CO2 cycloaddition with other epoxides.Additionally, the mechanistic details for the fixation of CO2 into cyclic carbonate catalyzed by SBA-15/KI and Zn-SBA-15/KI were also contrastively elucidated using the density functional theory (DFT) method. The DFT results suggested that zincmodified and unmodified catalysts showed different coupling modes of CO2, and the ‡ These authors contributed equally to this work. -2-ring-opening reaction was the rate-determining step in the SBA-15/KI catalyzed cycloaddition reaction, but the zinc-modified SBA-15/KI catalysts could enhance the CO2 cycloaddition as the formation of a stable complex which was beneficial to CO2 trapping. As a result, the ring-closing reaction became the rate-determining step in the Zn-SBA-15/KI catalyzed cycloaddition reaction, which were promising results to guide the catalyst design for CO2 conversion.

Periodic Mesoporous Organosilica with a Basic Urea‐Derived Framework for Enhanced Carbon Dioxide Capture and Conversion Under Mild Conditions

“…In addition, the structure of PMO-UDF was verifiedb yu sing solid-state NMR spectroscopy ( Figure 1B). The 29 Si magic-angle spinning( MAS) NMR spectrum showedt hree major signals centered at d = À110, À102, and À65 ppm, which correspond to the Si species of Q 4 [( SiO) 4 Si], Q 3 [( SiO) 3 Si(OR)] (R = Et or H), and the T 3 resonance from Si species attached to an organic group [ÀCH 2 ÀSi(OSi ) 3 ], respectively. [20] The spectrumd id not displaya ny other signals, which verified the complete integration of the organic precursor into the silica framework through the hydrolysis of terminal alkoxysilanes.…”

“…Firstly,t he order of the nucleophilicity is Br À > I À ;a saresult of the presence of hydrogen-bond donors in PMO-UDF-19, as tronger hydrogen-bond interaction was formed for Br À than I À ,w hich endowed I À with an enhanced leaving ability compared with Br À ,t herefore I À was more inclined to facilitatet he nucleophilic attack to open the epoxide ring, consistent with ap revious study. [28] Secondly,K + + can activate an epoxide throught he electrostatic interaction with Oa tom of epoxide and further stabilizet he ring-opened intermediate by forming ap otassium alkoxide compound, [29] whereas TBA + + is used to decompose to tributylamine as aC O 2 activatort og enerate ac arbamate salt. [30] The KI cocatalyst exhibited ab etter synergistic effect with PMO-UDF-19 than TBAI, which indicates that it is vital to proceedw ith the ring-opening step of epoxide comparedw ith CO 2 activation for the coupling reaction.…”

Zwitterionic Imidazole‐Urea Derivative Framework Bridged Mesoporous Hybrid Silica: A Highly Efficient Heterogeneous Nanocatalyst for Carbon Dioxide Conversion

“…N 2 adsorption–desorption isotherms and pore size distributions of the Im‐Si‐I‐ ϕ samples with different compositions are displayed in Figure . All the isotherms are of type IV with H1 hysteresis loops, which evidence their ordered mesoporous structure . The BET surface area and pore volume decrease gradually with an increase in the concentration of the imidazole‐urea derivative precursor IUP (Table ) because of the higher dispersion of IUP and its blocking of pores.…”

“…This was enhanced to 82–85 % at a higher pressure of 2.0–2.5 MPa (entries 13 and 10). If the CO 2 pressure was increased, reactant CO 2 molecules were more likely to be dissolved in the substrate PO phase, which would have a positive impact on the coupling of PO and CO 2 . If we consider the potential danger in practical production operated at high pressures, in this case a low CO 2 pressure of 2.5 MPa is sufficient for the synthesis of PC.…”

Efficient Solvent‐Free Carbon Dioxide Fixation Reactions with Epoxides Under Mild Conditions by Mixed‐Ligand Zinc(II) Metal–Organic Frameworks

“…However, limitations of product separation and catalyst recycling are of real concern in the homogeneous catalytic reaction. These limitations have been tackled to a great extent by the utilization of heterogeneous catalysts that include metal oxides, coordination complexes, zeolites, and functional polymers, which display a low activity under ambient conditions or leaching …”