Photothermal Conversion of CO₂ into CH₄ with H₂ over Group VIII Nanocatalysts: An Alternative Approach for Solar Fuel Production

Abstract

The photothermal conversion of CO 2 provides a straightforward and effective method for the highly efficient production of solar fuels with high solar-light utilization efficiency. This is due to several crucial features of the Group VIII nanocatalysts, including effective energy utilization over the whole range of the solar spectrum, excellent photothermal performance, and unique activation abilities. Photothermal CO 2 reaction rates (mol h À1 g À1 ) that are several orders of magnitude larger than those obtained with photocatalytic methods (mmol h À1 g À1 ) were thus achieved. It is proposed that the overall water-based CO 2 conversion process can be achieved by combining light-driven H 2 production from water and photothermal CO 2 conversion with H 2 . More generally, this work suggests that traditional catalysts that are characterized by intense photoabsorption will find new applications in photo-induced green-chemistry processes.How to provide clean, affordable, and reliable energy without causing climate change is a common concern in the world. [1] The conversion of CO 2 , the major component of greenhouse gas, into renewable hydrocarbon fuels by solar energy provides a sustainable way for carbon cycling, and is of significance in solving both energy and environmental issues. Today, solar fuel production by CO 2 conversion is mainly achieved according to two approaches: The first approach is based on photocatalytic CO 2 conversion over semiconductors, using photoexcited e À /h + to drive the simultaneous processes of water photooxidation (at the valence band) and CO 2 photoreduction (at the conduction band). [2] However, photocatalytic CO 2 conversion remains very inefficient because of the kinetic limitations of multiple e À /H + transfer processes and the limited abilities of traditional semiconductors to activate thermodynamically stable CO 2 molecules. [3] According to recent results, [2,4] the reaction rates of photocatalytic CO 2 conversion processes using H 2 O or H 2 as the hydrogen source are on the order of mmol h À1 g À1 , even leaving aside the uncertainty of the carbon source of the final reduction products (the observed products possibly originate from the photoreforming of residual carbonaceous substances rather than the photoreduction of CO 2 ). The second approach makes use of the dissociation of CO 2 by two-step thermochemical cycles of metal oxide redox pairs (mainly Zn/ZnO, Ce 2 O 3 /CeO 2 , FeO/Fe 3 O 4 , and SnO/SnO 2 ); these cycles are driven by the heat obtained from concentrated solar radiation. [5] However, the very high operation temperature (nearly 2000 8C) and special reactor design are indispensable to realize this reaction. More convenient methods for lightdriven CO 2 conversion, especially for water-based CO 2 conversion, a process that mimics photosynthesis, are urgently required.The recently emerged photothermal effect (or rapid heating) of nanometals inspired us to seek new methods for the production of solar fuels. The photothermal effect of nanometals stems from the di...

Thermo‐Photocatalysis: Environmental and Energy Applications

“…[2] Moreover,t his concept is stated to be an important pathway to harvesta nd use solar energy for ab road range of energy applications, as well as environmental pollution remediation and water distillation and desalination. [6][7][8] This represents an opportunity for researchers workingi ntraditional photocatalysis and thermocatalysis to diversify and exploit synergistic catalysis to solve the negative aspects of the individual catalytic processes while also increasing the usage of the solar energy.…”

Sustainability and Nanomaterials in Concert

“…The choice of alumina as inert support was critical to independently establish the photothermal effect of the metal nanoparticles and distinguish it from mere photocatalysis. All explored metals showed remarkable activity in a broad range of wavelengths …”

FeO–CeO2 nanocomposites: an efficient and highly selective catalyst system for photothermal CO2 reduction to CO

“…In photothermal catalysis, strong absorption of solar photons by the catalyst results in catalyst heating to temperatures up to 450°C, thus allowing traditional thermal catalytic processes to occur at reasonable rates [28][29][30] . Recently, Ye and coworkers reported photothermal CO 2 hydrogenation to CH 4 with good efficiency and selectivity over a series of group VIII nanocatalysts 31 . Subsequently, Zhang and coworkers reported photothermal CO 2 hydrogenation to C 2+ hydrocarbons using an alumina-supported Co-Fe alloy nanoparticle catalyst 30 .…”