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Pd-Based heterogeneous catalysts possess excellent activity for direct esterification of CO to dimethyl oxalate (DMO), and lots of investigations have been conducted on the active component Pd. Nevertheless, there are few studies on the effect of the support structure on its catalytic performance. The cationic regulation of the spinel-like oxide Zn–Al–O support with a clear structure increased the activity of the catalyst from 48.4% to 63.7%. It was found that there are few oxygen defects in the pure support, but a large number of oxygen defects appear in the reduced catalyst, and their number is positively correlated with the Zn/Al ratio of the support. A large number of oxygen defects make the valence state of the active metal lower, which improves the activity of the catalyst. This work provides evidence revealing the favorable effect of the catalyst support on the direct esterification of CO to DMO.

Rare-earth infrared nonlinear optical (IR NLO) compounds have garnered significant attention due to their abundant electronic structures. However, their NLO efficiency has been relatively modest, attributed to the localization of valence electron shells in rare-earth metals. Traditional design strategies for IR NLO materials have predominantly focused on MQ4(M= metal, Q= S or Se) tetrahedra, with limited exploration of MQ6octahedra. We introduce a novel approach to enhance NLO effects by incorporating distorted mixed anionic octahedral M(S/X)6groups. To illustrate this strategy, we undertake structure modification and optimization of IR NLO performance using the Y–Ga–Ge–S system as an example. The synthesis of a new rare-earth chalcogenide, Y6Ga2GeS14(1), serves as a foundation. Further halogen atom substitution yields Y6Ga4.2S13.6Cl3.4(2), Y6Ga2.83Ge2S16.75Cl (3), and Y6Ga2.83Ge2S16.5Br1.5(4). All compounds demonstrate remarkable NLO performance, including moderate NLO coefficients (0.17–0.70 × AgGaS2), large laser-induced damage thresholds (LIDTs) (3.78–6.19 × AgGaS2), and a broader transmission range (0.5–14.9 μm). The incremental enhancement of NLO efficiency in compounds 1–4can be attributed to symmetry breaking induced by halogen atom substitution and increased distortion of the octahedral M(S/X)6motifs in their structures, validating the effectiveness of our strategy. Notably, this strategy concurrently increases the band gap and LIDT, overcoming the NLO–LIDT incompatibility, being strikingly different from other reported approaches. This work provides new insights into optimizing the NLO performance of rare-earth IR NLO compounds through the modulation of octahedral motifs.

The diamond-like structure is characterized by the well-arranged parallel tetrahedral units, which hold significant importance for infrared nonlinear optical (NLO) applications. By employing an unconventional substitution strategy, a diamond-like ZnS (sphalerite) template was utilized to replace the several ZnxSytetrahedra with one-dimensional [Na2PbI] infinite chains, resulting in the successful design and synthesis of a salt-inclusion sulfide, [Na2PbI][Ga7S12] (1). Remarkably, the highly parallel-oriented [Ga7S16] double T2-supertetrahedron units and the presence of Pb2+-centered polyhedra contribute to its exceptional second-harmonic generation (SHG) intensity (2.6 × AgGaS2@1800 nm), belonging to the top-performing in salt-inclusion chalcogenides. Furthermore, compound 1possesses an appropriate band gap (Eg= 2.53 eV) and exceeds the two-photon absorption of 1064 nm, mainly resulting in a high laser-induced damage threshold (LIDT, 3.6 × AgGaS2). Particularly, phase 1achieves a phase-matching ability (birefringence: 0.069) that template α-ZnS cannot possess. These characteristics indicate that this unconventional substitution strategy provides insights into the design of excellent diamond-like NLO compounds.

Enhancement of the nonlinear optical (NLO) output power of lasers requires urgent development of an NLO crystal with a significant second-harmonic generation (SHG) response and sufficient birefringence for phase-matching capability; however, simultaneously optimizing these two key parameters remains a great challenge. In contrast to traditional single-anion units, the stereochemically-active lone pair Sb3+ion is coordinated by S2−and I−ions to yield the mixed-anionic SbSI chalcohalide that can enhance hyperpolarizability and anisotropic polarizability concurrently. As anticipated, SbSI exhibited the largest SHG response (5.7 × AgGaS2@1.91μm) among phase-matching Sb-based sulfides, the favorable laser-induced damage threshold (LIDT, 2.3 × AgGaS2@2.09μm), and the giant calculated birefringence (0.62@1.91 μm). Structural analysis and computational simulations indicate that the highly polarizable mixed anion determine the enormous SHG response and birefringence.