Effective Low-Temperature Methanol Aqueous Phase Reforming with Metal-Free Carbon Dots/C₃N₄ Composites

Abstract

Methanol aqueous phase reforming (MAPR) reaction under mild conditions is one of the most practical ways to generate hydrogen (H2), in which the liquid vaporization unit could be removed by the water phase reforming, making the structure of an in situ H2 production reactor more compact. In this work, the H2 production performances of the metal-free catalyst, N-doped carbon dots/g-C3N4 (NCDs/g-C3N4; CN-x) composites, was investigated for the MAPR reaction under low temperature and normal pressure. The optimized metal-free catalyst (NCDs/g-C3N4; CN-0.7) displays a H2 yield of 19.5 μmol g–1 h–1 at 80 °C. More importantly, a clear understanding on the effective MAPR reaction at low temperature and normal pressure was acquired from in situ diffuse reflectance FTIR spectroscopy and the transient photovoltage test. The introduction of NCDs leads to the localization of surface charge, which is beneficial to the selective adsorption and polarization activation of polar molecules on the catalyst surface. This work provides a new strategy for the carbon-based catalyst design of the MAPR reaction at low temperatures.

CO-Free H2 Production by Aqueous-Phase Reforming of Methanol Utilizing Heterogenized Ru-MACHO at Low Temperature

“…In 2013, Nielsen et al published an aqueous-phase reforming of methanol (APRM) method that employed homogeneous Ru-MACHO under 100 °C, resulting in a maximum TOF of 2670 and 350,000 TON for 600 h, without generating CO . Since the publication, there has been investigation into APRM using a homogeneous catalyst. − ,− However, the homogeneous nature of the Ru-MACHO catalyst poses difficulties in separation, resulting in significant challenges for its industrial application. ,− Due to the advantage of a heterogeneous catalyst in separation, studies have been conducted using various transition metals in APRM with heterogeneous catalysts, but most of them require high temperatures (>200 °C) yet. ,− Therefore, demonstrating the activity of heterogeneous catalysts under mild conditions (<100 °C) like Ru-MACHO remains a significant challenge in the effective application of fuel cell systems.…”

Carbon-Dots-Modified Hierarchical ZnIn2S4/Ni–Al LDH Heterojunction with Boosted Charge Transfer for Visible-Light-Driven Photocatalytic H2 Evolution

“…Thus, the coupling of ZnIn 2 S 4 and Ni–Al LDH can predictably construct an efficient heterojunction to promote photocatalytic hydrogen production . Furthermore, the carbon dots (CDs) as a new type of 0D metal-free alternative are often used as electron mediators to enhance the photocatalytic activity in heterojunction catalysts on account of less toxicity, size effect, and excellent charge transfer ability. − In addition, CDs as a cocatalyst can effectively utilize the full spectrum of solar light and possess abundant active sites for photocatalytic H 2 generation . Consequently, CDs modify the ZnIn 2 S 4 /Ni–Al LDHs to construct a ternary catalytic system, which can overcome the rapid charge recombination and boost the electron transfer efficiency.…”

“…30−34 In addition, CDs as a cocatalyst can effectively utilize the full spectrum of solar light and possess abundant active sites for photocatalytic H 2 generation. 35 to construct a ternary catalytic system, which can overcome the rapid charge recombination and boost the electron transfer efficiency.…”

The Nature of Interfacial Catalysis over Pt/NiAl2O4 for Hydrogen Production from Methanol Reforming Reaction

“…Different reaction pathways of methanol reforming have been proposed in the literature, such as methanol dehydrogenation followed by the water–gas shift (WGS) reaction (CO intermediates), ,,,− the methyl-formate pathway, ,,, and the formate pathway. , although a formate species were detected by in situ DRIFTS, it was known as a spectator under similar reaction conditions following the “CO 2 + n H 2 → CH 3 OH” process. − Nowadays, several kinetic models of methanol reforming have been established based on respective elementary steps and surface species proposed. ,− For example, Jiang et al established a Langmuir–Hinshelwood model to describe the reaction process on methanol steam reforming over Cu/ZnO/Al 2 O 3 , while only one type of active site was taken into consideration. At the same time, Dümpelmann et al proposed that the rate-determining step (RDS) for methanol steam reforming is the step between adsorbed formaldehyde and O* or the empty site, and the RDS for WGS is the reaction between CO and hydroxyls to produce the formate species .…”