Two novel zeotype crystals, K4[Cr30（H2O） 3（OOCH） 6] 2[ P2W18O62]· 9.5H2 O and K4[ Cr3O（ H2O）3（ OOCH）6 ]2[ H3 P2 W17Co（H2O） O61]· 20H2O（2） , were synthesized and their structures were determined ...Two novel zeotype crystals, K4[Cr30（H2O） 3（OOCH） 6] 2[ P2W18O62]· 9.5H2 O and K4[ Cr3O（ H2O）3（ OOCH）6 ]2[ H3 P2 W17Co（H2O） O61]· 20H2O（2） , were synthesized and their structures were determined using X-ray single crystal diffraction. Crystal data： C12H43O103.5K4Cr6P2W18（1）, hexagonal P6（3）/m, α= 1. 5895（2） nm, b=1.5895（2） nm, c =2.1620（4） nm, α=90°, β=90°, γ= 120°, V=4.7305（13） nm^3, Z=2, R1 =0,0726, ωR2 =0. 1542; C6H57O98K4Cr3CoP2W17 （2）, hexagonal P6（3）/mmc, α = 1.61328（3） nm, b = 1.61328（3） nm, c=2.06613（9） nm, α=90°, β=90°, γ=120°, V=4.6570（2） nm^3, Z=2, R1 =0.0377, ωR2 =0. 1070. These crystals were characterized using elemental analysis, IR, TG-DTA, and XRD. It was found that the polyoxometalate anions maintained Wells-Dawson structure for crystal I and laeunary Wens-Dawson structure for crystal 2. Thermal analysis showed that crystal 1 lost the water of crystallization at 132 ℃, whereas crystal 2 lost the water of crystallization at 100 ℃. Crystal 1 could reversibly desorb and adsorb water molecules and its crystal structure could be restored after re-adsorbing the water molecules. It was also found from the XRD patterns that the void size of crystal 2 is smaller compared with that of crystal 1, which is attributed to the higher anion charges.展开更多
The reaction mechanism of zeolite- or zeotype-catalyzed methanol-to-olefins（MTO） conversion is still a subject of debate. Employing periodic density functional theory calculations, the olefin-based cycle was studied...The reaction mechanism of zeolite- or zeotype-catalyzed methanol-to-olefins（MTO） conversion is still a subject of debate. Employing periodic density functional theory calculations, the olefin-based cycle was studied using tetramethylethene（TME） as a representative olefinic hydrocarbon pool in H-SAPO-18 zeotype. The overall free energy barrier at 673 K was calculated and found to be less than 150 kJ/mol in the TME-based cycle, much lower than those in the aromatic-based cycle（〉 200 kJ/mol）, indicating that olefins themselves are the dominant active hydrocarbon pool species in H-SAPO-18. The similarity of the intermediates involved between the aromatic-based cycle and the olefin-based cycle was also highlighted, revealing that both cycles were pattern-consistent. The selectivity related to the distribution of cracking precursors, such as higher olefins or carbenium ions, as a result of the olefin-based cycle for the MTO conversion. The enthalpy barrier of the crack-ing step scaled linearly with the number of carbon atoms of cracking precursors to produce ethene or propene with ethene being much less favored than propene for cracking of C7 and higher pre-cursors. This work highlighted the importance of the olefin-based cycle in H-SAPO-18 for the MTO conversion and established the similarity between the olefin-based and aromatic-based cycles.展开更多
基金Supported by the Dalian Municipal Science and Technology Commission and Liaoning Provincial Science and Technology Com-mission(No. 20031059)
文摘Two novel zeotype crystals, K4[Cr30（H2O） 3（OOCH） 6] 2[ P2W18O62]· 9.5H2 O and K4[ Cr3O（ H2O）3（ OOCH）6 ]2[ H3 P2 W17Co（H2O） O61]· 20H2O（2） , were synthesized and their structures were determined using X-ray single crystal diffraction. Crystal data： C12H43O103.5K4Cr6P2W18（1）, hexagonal P6（3）/m, α= 1. 5895（2） nm, b=1.5895（2） nm, c =2.1620（4） nm, α=90°, β=90°, γ= 120°, V=4.7305（13） nm^3, Z=2, R1 =0,0726, ωR2 =0. 1542; C6H57O98K4Cr3CoP2W17 （2）, hexagonal P6（3）/mmc, α = 1.61328（3） nm, b = 1.61328（3） nm, c=2.06613（9） nm, α=90°, β=90°, γ=120°, V=4.6570（2） nm^3, Z=2, R1 =0.0377, ωR2 =0. 1070. These crystals were characterized using elemental analysis, IR, TG-DTA, and XRD. It was found that the polyoxometalate anions maintained Wells-Dawson structure for crystal I and laeunary Wens-Dawson structure for crystal 2. Thermal analysis showed that crystal 1 lost the water of crystallization at 132 ℃, whereas crystal 2 lost the water of crystallization at 100 ℃. Crystal 1 could reversibly desorb and adsorb water molecules and its crystal structure could be restored after re-adsorbing the water molecules. It was also found from the XRD patterns that the void size of crystal 2 is smaller compared with that of crystal 1, which is attributed to the higher anion charges.
基金supported by the National Key Research and Development Program of China (2016YFB0701100, 2017YFB0702800)the National Natural Science Foundation of China (21673295)~~
文摘The reaction mechanism of zeolite- or zeotype-catalyzed methanol-to-olefins（MTO） conversion is still a subject of debate. Employing periodic density functional theory calculations, the olefin-based cycle was studied using tetramethylethene（TME） as a representative olefinic hydrocarbon pool in H-SAPO-18 zeotype. The overall free energy barrier at 673 K was calculated and found to be less than 150 kJ/mol in the TME-based cycle, much lower than those in the aromatic-based cycle（〉 200 kJ/mol）, indicating that olefins themselves are the dominant active hydrocarbon pool species in H-SAPO-18. The similarity of the intermediates involved between the aromatic-based cycle and the olefin-based cycle was also highlighted, revealing that both cycles were pattern-consistent. The selectivity related to the distribution of cracking precursors, such as higher olefins or carbenium ions, as a result of the olefin-based cycle for the MTO conversion. The enthalpy barrier of the crack-ing step scaled linearly with the number of carbon atoms of cracking precursors to produce ethene or propene with ethene being much less favored than propene for cracking of C7 and higher pre-cursors. This work highlighted the importance of the olefin-based cycle in H-SAPO-18 for the MTO conversion and established the similarity between the olefin-based and aromatic-based cycles.
