Boosting Interfacial Electron Transfer between Pd and ZnTi-LDH via Defect Induction for Enhanced Metal-Support Interaction in CO Direct Esterification Reaction.

Strong metal-support interaction is crucial to the stability of catalysts in heterogeneous catalysis. However, reports on boosting interfacial electron transfer between metal and support via defect induction for enhanced metal-support interaction are limited. In this work, ultrathin reducible ZnTi-layered double hydroxide (LDH) nanosheets with rich oxygen defects were synthesized to stabilize Pd clusters, and the rich oxygen defects promoted Pd cluster bonding with Zn and Ti atoms in supports, thereby forming a metal-metal bond. Electron spin resonance (ESR), X-ray absorption fine spectra (XAFS), and density functional theory (DFT) calculations demonstrate remarkable interfacial electron transfer (0.62 e). The Pd/ZnTi-LDH catalyst shows superior catalytic stability for CO direct esterification to dimethyl oxalate. By contrast, the nonreducible Pd/ZnAl-LDH catalyst with a few oxygen defects shows minimal interfacial electron transfer (0.08 e), which leads to relatively poor catalytic stability. This work provides a deep insight into promoting the stability of catalysts by boosting interfacial electron transfer via defect induction.

Zn2+ stabilized Pd clusters with enhanced covalent metal-support interaction via the formation of Pd-Zn bonds to promote catalytic thermal stability.

Pd-Based heterogeneous catalysts have been demonstrated to be efficient in numerous heterogeneous reactions. However, the effect of the support resulting in covalent metal-support interaction (CMSI) has not been researched sufficiently. In this work, a Lewis base is modulated over MgAl-LDH to investigate the support effects and it is further loaded with Pd clusters to research the metal-support interactions. MgAl-LDH with ultra-low Pd loading (0.0779%) shows CO conversion (55.0%) and dimethyl oxalate (DMO) selectivity (93.7%) for CO oxidative coupling to DMO, which was gradually deactivated after evaluation for 20 h. To promote the stability of Pd/MgAl-LDH, Zn2+ ions were introduced into the MgAl-LDH support to strengthen the CMSI by forming Pd-Zn bonds, which further increased the adsorption energy of the Pd clusters on ZnMgAl-LDH, and this was verified by X-ray absorption fine structure (XAFS) measurements and density functional theory (DFT) calculations. The stability of the Pd/ZnMgAl-LDH catalyst could be maintained for at least 100 h. This work highlights that covalent metal-support interactions can be strengthened by forming new metal-metal bonds, which could be extended to other systems for the stabilization of noble metals over supports.

Proton-conducting layered structures based on transition metal oxo-clusters supported by Sb(iii) tartrate scaffolds.

Two transition metal-antimony oxo-cluster based compounds, H5{MCd(H2O)6[M(H2O)3Co3SbVSb(µ3-O)8(l-tta)6]}·7H2O (1) (M = Cd0.5 + Co0.5) and H3K5(H2O)11{Cd(H2O)4[Cd(H2O)Fe4Cd2Sb6(µ4-O)5(µ3-O)3(l-tta)6][Cd(H2O)2Fe4Cd2Sb6(µ4-O)4(µ3-O)4(l-tta)6][Cd(H2O)2Fe4Cd2Sb6(µ4-O)4(µ3-O)4(l-tta)6Cd(H2O)5]}·17H2O (2) (L-H4tta = l-tartaric acid) were hydrothermally synthesized and characterized. Compound 1 features a [MCo3SbVSb(µ3-O)8(l-tta)6(H2O)3]9- cluster, while compound 2 contains three types of clusters, namely, [Cd(H2O)Fe4Cd2Sb6(µ4-O)5(µ3-O)3(l-tta)6]4-, [Cd(H2O)2Fe4Cd2Sb6(µ4-O)4(µ3-O)4(l-tta)6]4- and [Cd(H2O)2Fe4Cd2Sb6(µ4-O)4(µ3-O)4(l-tta)6Cd(H2O)5]2-. All the clusters are of sandwich-type with {Sb3(µ3-O)(l-tta)} scaffolds on the top and bottom. The Cd (and M in 1) ions interconnect the clusters into layered structures in both compounds. To the best of our knowledge, this is the first report of transition metal-antimony oxo-clusters that simultaneously contain the first-row and second-raw transition metal ions, and compound 1 represents the first example of such type of clusters that contain Sb(v). The two compounds exhibit proton conductivity with the values of 2.43 × 10-3 and 2.95 × 10-3 S cm-1 at 85 °C under 98% relative humidity, respectively.

A hybrid of CdS/HCa2Nb3O10 ultrathin nanosheets for promoting photocatalytic hydrogen evolution.

A hybrid of CdS/HCa2Nb3O10 ultrathin nanosheets was synthesized successfully through a multistep approach. The structures, constitutions, morphologies and specific surface areas of the obtained CdS/HCa2Nb3O10 were characterized well by XRD, XPS, TEM/HRTEM and BET, respectively. The TEM and BET results demonstrated that the unique structural features of CdS/HCa2Nb3O10 restrained the aggregation of CdS nanoparticles as well as the restacking of nanosheets effectively. HRTEM showed that CdS nanocrystals of about 25-30 nm were firmly anchored on HCa2Nb3O10 nanosheets and a tough heterointerface between CdS and the nanosheets was formed. Efficient interfacial charge transfer from CdS to HCa2Nb3O10 nanosheets was also confirmed by EPR and photocurrent responses. The photocatalytic activity tests (λ > 400 nm) showed that the optimal hydrogen evolution activity of CdS/HCa2Nb3O10 was about 4 times that of the bare CdS, because of the efficient separation of photo-generated carriers.

Development and photocatalytic mechanism of monolayer Bi2MoO6 nanosheets for the selective oxidation of benzylic alcohols.

Monolayer Bi2MoO6 nanosheets have been successfully prepared for the first time via a bottom-top approach with surfactant assistance, and show 8 times higher activity than bulk Bi2MoO6 for the selective oxidation of benzyl alcohol. Ultrafast charge separation and more acid-base active sites on the monolayer nanosheets are considered to be responsible for the robust photoactivity.