Ethylene oligomerization on Ni²⁺ single sites within lacunary defects of Wells Dawson polyoxometalates

Abstract

In this work, the utilization of lacunary defects of Wells Dawson polyoxometalate (POM) as platforms to isolate single Ni2+ sites at the molecular level for ethylene oligomerization is reported.

Single-site, Ni-modified Wells–Dawson-type polyoxometalate for propylene dimerization

“…[54][55][56][57][58] Recently, we observed Ni-substituted Wells-Dawson-type POM (K 8 P 2 W 17 O 61 •Ni 2+ ) supported on SBA-15 (Ni-POM-WD/ SBA-15) was active for ethylene oligomerization without added co-catalyst. 59 Ni-POM-WD/SBA-15 achieved an ethylene consumption rate of 152 mmol g cat −1 h −1 (4.22 × 10 −5 mol g cat −1 s −1 ) at 200 °C and 2 MPa of ethylene partial pressure, which is comparable to reported Ni-based catalysts. 59 For instance, Ni-SiO 2 -Al 2 O 3 exhibited ethylene oligomerization rates of 0.7-2.7 × 10 −5 mol g cat −1 s −1 at 170-230 °C and 1.5-3.5 MPa.…”

“…31 P NMR peaks at these locations correspond to successful metalation of the lacunary POM-WD by Ni. [57][58][59]63 From our previous studies, single crystal XRD of Ni-POM-WD crystals indicates that the Ni sites substitute one of the three tungsten atoms in capping regions of a WD POM, eliminating the probability of the Ni sites being outside of the defect position. 59 In addition, Ni loading of unsupported Ni-POM-WD obtained by ICP corresponds to the nominal loading.…”

“…59 In addition, Ni loading of unsupported Ni-POM-WD obtained by ICP corresponds to the nominal loading. 59 SBA-15 was prepared using the synthesis procedures described elsewhere. 65,66 First, 18 g of Pluronic 123 (Sigma-Aldrich) and 99.5 g of hydrochloric acid (Millipore Sigma, 37%) were fully dissolved in 550 g of deionized water.…”

“…In addition, Ni-POM-WD/SBA-15 was successfully regenerated after ethylene oligomerization reaction via helium treatment at 300 °C. 59 Moreover, the dispersion of Ni-POM-WD on the support was shown to be critical, as the unsupported Ni-POM-WD showed no catalytic activity for ethylene oligomerization at 200 °C and 2 MPa due to inaccessibility to Ni sites in the unsupported crystals. 59 Here, we report the performance of a Ni-substituted Wells-Dawson POM for propylene dimerization.…”

“…59 Moreover, the dispersion of Ni-POM-WD on the support was shown to be critical, as the unsupported Ni-POM-WD showed no catalytic activity for ethylene oligomerization at 200 °C and 2 MPa due to inaccessibility to Ni sites in the unsupported crystals. 59 Here, we report the performance of a Ni-substituted Wells-Dawson POM for propylene dimerization. The catalytic performance, regenerability, and the kinetic parameters of Ni sites on Ni-POM-WD/SBA-15 for propylene dimerization were determined and compared to literature reports.…”