Controllable Visible-Light-Driven Syngas Evolution by a Ternary Titania Hybrid Sacrificial System with a Photosensitive Metal–Organic Pd^II Cage and Re^I Catalyst

Abstract

A photosensitive metal–organic cage (MOC), denoted as MOC-Q2, consisting of two Pd2+ metal ions and four tridentate ligands, is synthesized, and then MOC-Q2 is linked with titania to obtain a hybrid material TiO2-MOC-Q2, which exhibits remarkable photocatalytic H2 evolution activities. After loading a molecular Re catalyst, the ReP/TiO2-MOC-Q2 (6.5 wt %) photocatalyst demonstrates a selective performance of CO2 reduction to CO in dry CO2-saturated dimethylformamide (DMF) solution. By adjusting only the water content in the reaction system, the ternary catalyst can produce syngas with controlled ratios of CO/H2 varying from 15:1 to 1:2. CO/H2 gas evolution rates of 638/604 and 499/964 μmol g–1 h–1 are gained with a CO/H2 ratio of 1:1 and 1:2 in 5 h experiments, respectively. And the corresponding TONCO/TONH2 in the 20 h persistence test is calculated to be 875/458. This system presents one of the best activities among the reported syngas production photocatalysts without using noble ruthenium complexes. This work provides a promising way for the development of multifunctional heterogeneous MOC-based photocatalysts.

Isoreticular Preparation of Tetraphenylethylene‐based Multicomponent Metallacages towards Light‐Driven Hydrogen Production

“…Metallacage 4 e produced about 47.1 μM H 2 during test, and the H 2 generation rate was calculated to be 1707 μmol g À 1 h À 1 , which is one of the highest values among reported metallacages (Table S7). [39][40][41][42] The turnover number (TON) and apparent quantum yield (AQY) were 157 and 6.53×10 À 3 , respectively. Compared to metallacage 4 d, the hydrogen production rate increased over threefold, suggesting the importance of the introduction of additional [64] catalytic metal complexes in efficient hydrogen evolution reactions.…”

“…Metallacages, [13–38] as the discrete analogues of MOFs, not only possess the above‐mentioned advantages, but also exhibit well‐defined and tunable nanoscale structures, which can facilitate directed electron or energy transfer within the metallacages and thus increase the photocatalytic activity. However, the development of metallacage‐based light‐driven hydrogen production systems is far less behind that of MOFs [39–43] . This is because that for most metallacages, the metal nodes are designed to be fully coordinated to avoid the formation of thermodynamic mixtures, resulting in the lack of unsaturated metal centers for photocatalysis [44–45] .…”

Mixed-Blocks-Driving Nickel–Porphyrin Covalent Organic Polymers for Photocatalytic Syngas Production from CO2 with Fine Selectivity

“…At present, a large number of methods and techniques are being investigated around the sticking point of precisely regulating the syngas ratio. As depicted in Scheme , the realized methods to control the syngas ratio are boiled down to three types, including regulating the component ratio of composite materials, ,− the atomic content of a single-material catalyst, ,, and the composition of solvents (Scheme A). For instance, Song et al controlled the heterojunction concentration of CoAl-LDH/MoS 2 materials by the dint of the advantage of LDHs for CO 2 adsorption and activation, realizing syngas ratios (CO/H 2 ) from 1:1.3 to 1:15 .…”

“…Also, the syngas ratio can be tuned through building defects (O, S, or N vacancy) or the atomistic ratio of a single-crystal material, such as Zn X Cd 1‑ X S . Furthermore, considering that H 2 O serves as the main participant of the whole reaction system, supplying hydrogen proton and influencing the system viscosity and conductivity, variation of the H 2 O amount is also an important parameter to modulate the CO/H 2 ratio. , Although regulation of syngas in photocatalysis has progressed, most works have focused on inorganic semiconductor materials, but the catalytic activity is still kept at a low level, which is attributed to limited compositional flexibility and deficient active sites. In recent years, covalent organic polymer (COP) semiconductors have gained particular attention by virtue of their earth-abundance (C, H, O, N, and S), structural customization, and functional diversities.…”

Regulating CO and H2 Ratios in Syngas Produced from Photocatalytic CO2/H2O Reduction by Cu and Co Dual Active Centers on Carbon Nitride Hollow Nanospheres

“…In the study of photocatalytic syngas generation, various techniques have been used to adjust the H 2 /CO ratio in syngas, including controlling the amount of water − and adjusting the catalyst composition (involves changing the amount of cocatalyst, − changing the ratio of components in the composite catalyst, ,− controlling the defect content, , interface engineering, changing the size of the active center, , microenvironmental modulation of the active site, and introducing dual cocatalysts and adjusting their ratio and content). , The CO 2 reduction reaction (CO 2 RR) and hydrogen evolution reaction (HER) are both two-electron reduction reactions, and they are competitive reactions. The reactions involved are as follows: CO 2 + 2 normalH + + 2 normale − → CO + normalH 2 normalO goodbreak0em1em⁣ italicE 0 = prefix− 0.53 nobreak0em0.25em⁡ normalV .25em vs. nobreak0em0.25em⁡ NHE .25em at .25em pH = 7 2 normalH 2 normalO + 2 normale − → 2 OH − + normalH 2 goodbreak0em1em⁣ italicE 0 = 0 nobreak0em0.25em⁡ normalV .25em <...…”