Polyethylene terephthalate (PET) is selectively depolymerized by a carbon-supported single-site molybdenum-dioxo catalyst to terephthalic acid (PTA) and ethylene. The solventless reactions are most efficient under 1 atmosphere of H 2. The catalyst exhibits high stability and can be recycled multiple times without loss of activity. Waste beverage bottle PET or a PET + polypropylene (PP) mixture (simulating the bottle + cap) proceeds at 260 8C with complete PET deconstruction and quantitative PTA isolation. Mechanistic studies with a model diester, 1,2-ethanediol dibenzoate, suggest the reaction proceeds by initial retro-hydroalkoxylation/b-CÀO scission and subsequent hydrogenolysis of the vinyl benzoate intermediate. Polymer-based plastics are among the most widely used synthetic materials worldwide and are essential for modern life and the global economy. By 2050, their annual production should reach % 1.12 billion tons. [1] Since almost all plastics are produced from fossil feedstocks their impact on finite natural resources is a concern, as is waste plastic accumulation and the worldwide environmental consequences. [2] Underlying this accumulation is a linear economic model whereby most products are discarded after use. In contrast, a circular economy in which waste plastics are recycled and repurposed is far more rational. [3] Due to the great popularity of polyesters, there is a rising need for their recycling. Current technologies are: 1) Thermomechanical recycling in which sorted polyethylene terephthalate (PET) waste is remelted and reprocessed. The high temperatures lead to significant thermal degradation, and lower grade plastics with inferior optical, thermal, and mechanical properties. 2) Chemical recycling in which one or more component monomers is recovered. [4] The attraction here is that valuable monomers can be repurposed for known or new materials having identical or higher performance. The most common chemical process for polyesters such as PET is glycolytic, methanolytic, or hydrolytic trans-esterification. These are catalyzed by metal acetates, [5] titanium complexes, [6] metal chlorides, [7] metallic [8] and metal oxide nanoparticles, [9] ionic liquids, [10] and bases. [11] Hydrosilylation [12] and microbial agents [13] were recently shown to also affect PET deconstruction. The principal limitation of such processes is formation of difficultly separated side products and the requirement of large solvent and degradation agent excesses (Figure 1 A). In principal, catalytic hydrogenolysis is attractive for deconstructing polyesters, however, there has been limited research. Recently, homogeneous Ru pincer complexes, such as Milsteins catalyst, [14] and Ru complexes with tridentate phosphine ligands, LRu(tmm) (L = triphos, triphos-xyl, tmm = trimethylenemethane), [15a] were shown to catalyze PET hydrogenolysis to the corresponding alcohols. [15] Although H 2 is a cost-effective reductant, these processes require high H 2 pressures, long reaction times (16-48 h), use of solvents, and expensive, ai...

The use of alternative oxidants for the oxidative dehydrogenation of propane (ODHP) is a promising strategy to suppress the facile overoxidation to COx that occurs with O2. Gaseous disulfur (S2)...

Ethylene remains one of the most valuable chemical feedstocks. Currently the industrial conversion of ethane to ethylene is achieved largely by steam cracking. The catalytic, highly exothermic oxidative dehydrogenation (ODH) of ethane with O2 is a challenging alternative that has been extensively studied on the laboratory scale. Here we investigate the possibility of using disulfur (S2) vapor as a thermodynamically “soft” oxidant for catalytically converting ethane to ethylene (“SODH”). Investigating a series of four catalysts we report a maximum ethylene yield of 76 % over an earth‐abundant FeSx‐based catalyst (maximum 90.2 % C2H4 selectivity at 820 °C). Yield and selectivity are stable for 50 hours on stream. The SODH rate law is 1st order in ethane and 1/2 order in S2, supporting a proposed Mars van Krevelen‐like mechanism at temperatures <700 °C. Furthermore, conversion and selectivity become insensitive to catalyst identity at temperatures >860 °C, suggesting the intrusion of radical pathways.