Making Persistent Plastics Degradable

The vastness of the scale of the plastic waste problem will require a variety of strategies and technologies to move toward sustainable and circular materials. One of these strategies to address the challenge of persistent fossil-based plastics is new catalytic processes that are being developed to convert recalcitrant waste such as polyethylene to produce propylene, which can be an important precursor of high-performance polymers that can be designed to biodegrade or to degrade on demand. Remarkably, this process also enables the production of biodegradable polymers using renewable raw materials. In this Perspective, current catalyst systems and strategies that enable the catalytic degradation of polyethylene to propylene are presented. In addition, concepts for using "green" propylene as a raw material to produce compostable polymers is also discussed.

Propylene synthesis via isomerization–metathesis of 1-hexene and FCC olefins

Highly efficient conversion of 1-hexene and FCC mixture to propylene via isomerization–metathesis (ISOMET) catalyzed by a HBEA–MoOx/Al2O3 system.

Direct transformation of butenes or ethylene into propylene by cascade catalytic reactions

Catalysts and processes involved in the direct conversion of ethylene or n-butenes into propylene are reviewed.

Effects of calcination and pretreatment temperatures on the catalytic activity and stability of H2-treated WO3/SiO2 catalysts in metathesis of ethylene and 2-butene

The effects of calcination and pretreatment temperatures of the H2-treated WO3/SiO2 catalysts in metathesis of ethylene and 2-butene to propylene were investigated. The results showed that pretreatment with pure hydrogen over the non-calcined catalysts resulted in higher activity and stability than the calcined catalysts, and the hydrogen pretreatment temperature at 650 °C offered the highest 2-butene conversion and propylene selectivity. The calcination of the catalyst before hydrogen pretreatment was proved to be unnecessary. As revealed by various characterization results from N2 physisorption, XRD, TEM, UV-Vis, Raman, in situ H2-TPR, in situ NH3-DRIFTS and in situ NH3-TPD techniques, activity of the metathesis of ethylene and 2-butene to propylene was related to tungsten dispersion on the support, WO2.83 and WO2 phase composition, and isolated surface tetrahedral tungsten oxide species. The stability of the metathesis reaction was also related to the total acidity and the acid sites of both Brønsted and Lewis acid sites.

Investigation on converting 1-butene and ethylene into propene via metathesis reaction over W-based catalysts

Supported W catalysts were extensively investigated for the conversion of 1-butene and ethylene into propene by metathesis reaction. The performance of catalysts was compared by using unsupported WO₃, pure SBA-15, supported W/SBA-15 with different W loadings, varied calcination temperatures, and by changing the pretreatment gas atmosphere. The above catalytic results could be employed to deduce the reaction mechanism combined with characterization techniques such as BET, XRD, UV-vis DRS, Raman, pyridine-IR, XPS, and H₂-TPR. In this study, over the investigated W/SBA-15 catalysts, the results showed that the silanol group (Si–OH) in SBA-15 could act as a weak Brønsted acid site for 1-butene isomerization. However, the metathesis reaction was catalyzed by W-carbene species. The initially formed W-carbenes (W Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CH–CH₃) as active sites were derived from the partially reduced isolated tetrahedral WO_x species which contained WO or W–OH bonds in W⁵⁺ species as corresponding Lewis or Brønsted acid sites. Furthermore, the W/SBA-15 being pretreated by H₂O led to a complete loss of the metathesis activity. This was mainly due to the sintering of isolated WO_x species to form an inactive crystalline WO₃ phase as demonstrated by XRD patterns. On the other hand, the reduction of WO_x species remarkably suppressed by H₂O pretreatment was also responsible for the metathesis deactivation. This study provides molecular level mechanisms for the several steps involved in the propene production, including 1-butene isomerization, W-carbene formation, and metathesis reaction.

The molecular level mechanism for conversion of 1-butene and ethylene into desired propene over W/SBA-15 catalysts has been elucidated.

Production of p-xylene from bio-based 2,5-dimethylfuran over high performance catalyst WO3/SBA-15

Mesoporous solid acid catalyst WO₃/SBA-15 possessing mainly Lewis acids exhibits high performance for the production of bio-based PX.