Continuous Room‐Temperature Hydrogen Release from Liquid Organic Carriers in a Photocatalytic Packed‐Bed Flow Reactor

Abstract

Despite the potential of hydrogen (H 2 ) storage in liquid organic carriers to achieve carbon neutrality, the energy required for H 2 release and the cost of catalyst recycling have hindered its large-scale adoption. In response, a photo flow reactor packed with rhodium (Rh)/titania (TiO 2 ) photocatalyst was reported for the continuous and selective acceptorless dehydrogenation of 1,2,3,4-tetrahydroquinoline to H 2 gas and quinoline under visible light irradiation at room temperature. The tradeoff between the reactor pressure drop and its photocatalytic surface area was resolved by selective in-situ photodeposition of Rh in the photo flow reactor post-packing on the outer surface of the TiO 2 microparticles available to photon flux, thereby reducing the optimal Rh loading by 10 times compared to a batch reactor, while facilitating catalyst reuse and regeneration. An example of using quinoline as a hydrogen acceptor to lower the energy of the hydrogen production step was demonstrated via the water-gas shift reaction.

Visible-Light-Mediated TiO2-Catalyzed Aerobic Dehydrogenation of N-Heterocycles in Batch and Flow

“…In a solid (TiO 2 )–liquid (the reaction solution)–gas (O 2 ) multiphasic reaction, the continuous flow process can also dramatically improve reactivity by increasing mass transfer and the surface-area-to-volume ratio by minimizing the head space . Using TiO 2 as a heterogeneous catalyst in a packed bed reactor can also increase the catalyst loading effect and make it easier to separate the catalyst after the reaction is complete, resulting in significantly shorter residence times and better recyclability. − Therefore, we focused on the use of a continuous flow process for our visible-light-mediated multiphasic reaction.…”

A Perspective Review on N-Heterocycles as Liquid Organic Hydrogen Carriers and Their Hydrogenation/Dehydrogenation Catalysts

“…025 wt % Rh/TiO 2 by selective in situ photodeposition of the noble metal Rh onto anatase-type TiO 2 in a photocatalytic flow reactor at room temperature and low pressure conditions. A sustainable and energy efficient photocatalytic strategy for THQ dehydrogenation with >98% yield and long-term stability and regeneration performance under continuous flow conditions for more than 72 h was achieved …”

Selective Photocatalytic Dehydrogenation of Formic Acid on Graphite Carbon Nitride with Dual-Sited Cobalt and Platinum Cocatalysts

“…Hydrogen has been emerging as the most promising alternative to fossil fuels to speed up the process of carbon neutrality . Compared to the traditional gray hydrogen generation, which involves high energy input and huge CO 2 release, photocatalysis holds prominent advantages in sustainability to produce green hydrogen. − Currently, photocatalytic hydrogen evolution from the aspect of hydrogen source could be mainly divided into three approaches: overall water splitting, hydrogen production in the presence of sacrificial agent, and splitting of other hydrogen carriers. − Considering the challenge in transportation of compressed hydrogen with low volumetric energy density, efficient hydrogen release from liquid organic hydrogen carriers by photocatalysis will promote the wide application of hydrogen. − …”