110th Anniversary: Near-Total Epoxidation Selectivity and Hydrogen Peroxide Utilization with Nb-EISA Catalysts for Propylene Epoxidation
Abstract: The Nb-EISA catalyst with relatively low Nb loadings (∼2 wt %) shows exceptional propylene epoxidation performance with H2O2 as oxidant at 30–40 °C, 5–9 bar propylene pressure with nearly total pro...
Summary (1 min read)
- Propylene oxide (PO) is one of the most important chemical intermediates for producing many essential fine chemicals, such as polyurethane plastics, polyglycol esters, unsaturated resins, and surfactants.
- While the TS-1 catalyst is active, it is expensive and undergoes deactivation.
- Hence, there continues to be interest in alternative PO processes using inexpensive and robust catalysts that maximize PO selectivity and H2O2 utilization.
- D ow nl oa de d vi a U N IV O F K A N SA S on M 32 Motivated by the foregoing considerations, the authors report here systematic investigations of Nb-EISA catalysts and their carbonized versions, C−Nb-EISA, for propylene epoxidation under similar operating conditions as those employed in the HPPO process.
2. EXPERIMENTAL SECTION
- Triblock copolymer (Pluronic P123, EO20− PO70−EO20, with an average molecular weight ∼5,800, Aldrich), ethanol (Absolute, 200 Proof, Acros organics), methanol (Sigma-Aldrich), tetraethyl orthosilicate (TEOS) (98% Acros organics), conc. hydrochloric acid (37%, Fisher), and niobium(V) chloride (Alfa Aesar) were used as received.
- Acetonitrile (HPLC grade, 99.9%, Fisher) and H2O2 (50 wt % in water, Fisher) were used as received for catalytic propylene epoxidation with H2O2.
- The Nb-EISA catalysts were prepared as described previously.
- 31 Briefly, TEOS was added to the acidified ethanolic solution containing P123, followed by the required amounts of niobium(V) chloride predissolved in ethanol.
- Thereafter, propylene was charged from an external reservoir pressurizing the reactor up to 0.9 MPa.
3. RESULTS AND DISCUSSION
- Detailed physicochemical characterization of Nb-EISA samples and their carbonized versions (C−Nb-EISA) may be found in the Supporting Information and elsewhere.
- Additionally, Nb-EISA catalysts prepared in two different batches with almost identical Nb loadings show similar catalytic activities (Table 2, entries 6 and 8) under similar reaction conditions.
- Nb-EISA catalysts with low Nb loadings (<2 wt %) exhibit excellent activity for propylene epoxidation displaying virtually total PO selectivity and H2O2 utilization toward PO formation with much reduced Nb leaching compared to Nb silicates prepared by impregnation and/or hydrothermal synthesis techniques.
- ■ ASSOCIATED CONTENT *S Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.9b03461.
- Schematic of experimental unit and figures for characterization of Nb-EISA and C−Nb-EISA (carbonized version) catalyst samples (PDF) ■ AUTHOR INFORMATION Corresponding Author *Phone: +1-785-864-2903.
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Q1. What have the authors contributed in "110th anniversary: near-total epoxidation selectivity and hydrogen peroxide utilization with nb-eisa catalysts for propylene epoxidation" ?
The Nb-EISA catalyst with relatively low Nb loadings ( ∼2 wt % ) shows exceptional propylene epoxidation performance with H2O2 as oxidant at 30−40 °C, 5−9 bar propylene pressure with nearly total propylene oxide ( PO ) selectivity ( > 99 % ), H 2O2 utilization ( > 99 % ) toward PO formation, high productivity ( ∼3200 mg/h/g ), and mild Nb leaching ( 3−6 % ) this paper.
Q2. What future works have the authors mentioned in the paper "110th anniversary: near-total epoxidation selectivity and hydrogen peroxide utilization with nb-eisa catalysts for propylene epoxidation" ?
This provides guidance for future work in developing new catalyst synthesis methods to achieve optimum hydrophobicity that minimizes catalyst leaching to practically viable levels. Density functional theory calculations were used to investigate catalytic pathways38 and probable reasons21 for hydrogen peroxide decomposition and potential metal leaching. If methanol is used as solvent, the propylene oxide can further undergo hydrolysis and solvolysis reactions to form the corresponding byproducts, propylene glycol and isomers of methoxy propanol, respectively. It is noteworthy that the reaction of the niobium silicate structure with H2O2 was modeled in different orientations 21 in order to understand the mechanism of H2O2 adsorption ( step 1 in Scheme 1 ), potential H2O2 decomposition, and metal leaching.