Directional-path modification strategy enhances PET hydrolase catalysis of plastic degradation.

Poly (ethylene terephthalate) (PET) is a widely used type of general plastic that produces a significant amount of waste due to its non-degradable properties. We propose a novel directional-path modification (DPM) strategy, involving positive charge amino acid introduction and binding groove remodeling, and apply it to Thermobifida fusca cutinase to enhance PET degradation. The highest value of PET degradation (90%) was achieved in variant 4Mz (H184S/Q92G/F209I/I213K), exhibiting values almost 30-fold that of the wild-type. We employed molecular docking, molecular dynamics simulations, and QM/MM MD for the degradation process of PET, accompanied by acylation and deacylation. We found that the distance of nucleophilic attack was reduced from about 4.6 Å in the wild type to 3.8 Å in 4Mz, and the free energy barrier of 4Mz dropped from 14.3 kcal/mol to 7.1 kcal/mol at the acylation which was the rate-limiting step. Subsequently, the high efficiency and universality of the DPM strategy were successfully demonstrated in LCC, Est119, and BhrPETase enhancing the degradation activity of PET. Finally, the highest degradation rate of the pretreated commercial plastic bottles had reached to 73%. The present study provides insight into the molecular binding mechanism of PET into the PET hydrolases structure and proposes a novel DPM strategy that will be useful for the engineering of more efficient enzymes for PET degradation.

Effect of point defects on acetylene hydrogenation reaction over Ni(111) surface: a density functional theory study.

Density functional theory (DFT) calculations are carried out to investigate the effect of point defects on acetylene hydrogenation reaction over Ni(111) surface with three different defect concentrations (DC = 0.0500, 0.0625, and 0.0833), compared with the perfect Ni(111) surface. The adsorptions of C2 species and H atoms and the mechanism of acetylene hydrogenation via the ethylene pathway are systematically analyzed. The results indicate that the existence of defects will make C2 species and H atoms more inclined to adsorb near the defects. Introducing an appropriate amount of point defect concentration can enhance the catalytic activity and ethylene selectivity of Ni. In this work, DC = 0.0625 Ni(111) surface has the highest catalytic activity and selectivity of ethylene. This work provides useful theoretical information on the effect of defects on acetylene hydrogenation and is helpful for the design of Ni and related metal catalysts with defects.

Theoretical study on the reaction mechanism and selectivity of acetylene semi-hydrogenation on Ni-Sn intermetallic catalysts.

Recently, Ni-Sn intermetallic compounds (IMCs) with unique geometric structures have been proved to be selective catalysts for acetylene hydrogenation to ethylene, but the origin of the selectivity remains unclear. In this work, a density functional theory (DFT) study has been carried out to investigate the mechanism of acetylene hydrogenation on six surfaces of Ni-Sn IMCs, and the geometric effects towards ethylene selectivity were revealed. Two key parameters (adsorption energy and the hydrogenation barrier of ethylene), which determine the ethylene selectivity, were studied quantitatively. The adsorption sites for C2Hy (y = 2, 3, 4) can be classified into three types: Type 1 (Ni3Sn(111) and Ni3Sn2(101)-2) with Ni trimers, Type 2 (Ni3Sn(001) and Ni3Sn2(001)) with Ni monomers, and Type 3 (Ni3Sn2(101) and Ni3Sn2(001)-2) with reconstructed metal trimers. The adsorption energy (Ead) decreases following the order: Type 1 > Type 3 > Type 2, which indicates that the adsorption strength depends significantly on site ensemble: a more isolated Ni site would facilitate the desorption of ethylene. However, the surface roughness mainly dominates the hydrogenation barrier of ethylene. Either low or high roughness decreases the interactions between H and C2H4 (Eint), resulting in an enhanced energy barrier for over-hydrogenation of C2H4 (Ea,hydr); while moderate roughness benefits Eint and lowers Ea,hydr. The selectivity to ethylene is denoted as ΔEa = Ea,hydr - |Ead|, thus depending on the interplay of site ensemble effects and surface roughness. From this point of view, Ni3Sn(001) and Ni3Sn2(101) surfaces with well-isolated Ni ensembles and low (or high) surface roughness exhibit decreased |Ead| and increased Ea,hydr, giving rise to excellent selectivity to ethylene. This work provides significant understanding of the origin of ethylene selectivity in terms of geometric effects, which gives helpful instruction for the design and preparation of intermetallic catalysts for acetylene semi-hydrogenation.

The reaction mechanism and selectivity of acetylene hydrogenation over Ni-Ga intermetallic compound catalysts: a density functional theory study.

Intermetallic compounds (IMCs) have shown excellent catalytic performance toward the selective hydrogenation of acetylene, but the theoretical understanding on this reaction over Ni-based IMCs is rather limited. In this work, the adsorptions of the C2 species, Bader charge, projected density of states (PDOS) and the reaction pathways were calculated by the density functional theory (DFT) method to investigate the mechanism and selectivity for the acetylene hydrogenation on the (111) surface of NinGa (n = 1, 3) IMCs, with a comparative study on the pristine Ni(111) surface. The results indicate that the adsorption energy of acetylene increased along with the Ni/Ga ratio, therefore a feasible acetylene adsorption on the Ga-rich surface guaranteed a low effective barrier, leading to the best activity for the NiGa(111) surface among three surfaces. Bader charge analysis shows that electrons transferred from Ga atoms to Ni atoms and further delivered to C2 species, decreasing the adsorption capacity of C2 species on NiGa(111) in comparison with those on Ni(111) and Ni3Ga(111). The reaction pathway of acetylene hydrogenation to ethylene via vinyl or even over-hydrogenation to ethane via ethyl is more favorable than the pathway involving the ethylidene intermediate on all surfaces. Moreover, the ethylene selectivity has a positive correlation with the gallium content by comparing the desorption barrier with the hydrogenation barrier of ethylene, thus the NiGa(111) surface also exhibits the best selectivity. Therefore, the NiGa(111) surface demonstrates to be an excellent reaction facet for the semihydrogenation of acetylene, which agreed with the experimental findings, and would provide helpful instructions for designing and preparing highly-selective and noble-substitute catalysts of alkyne semihydrogenation.