Solar Urea: Towards a Sustainable Fertilizer Industry

Abstract

Urea, an agricultural fertilizer, nourishes humanity. The century‐old Bosch–Meiser process provides the world's urea. It is multi‐step, consumes enormous amounts of non‐renewable energy, and has a large CO2 footprint. Thus, developing an eco‐friendly synthesis for urea is a priority. Herein we report a single‐step Pd/LTA‐3A catalyzed synthesis of urea from CO2 and NH3 under ambient conditions powered solely by solar energy. Pd nanoparticles serve the dual function of catalyzing the dissociation of NH3 and providing the photothermal driving force for urea formation, while the absorption capacity of LTA‐3A removes by‐product H2O to shift the equilibrium towards urea production. The solar urea conversion rate from NH3 and CO2 is 87 μmol g−1 h−1. This advance represents a first step towards the use of solar energy in urea production. It provides insights into green fertilizer production, and inspires the vision of sustainable, modular plants for distributed production of urea on farms.

Solar Urea: Towards a Sustainable Fertilizer Industry

“…[7] Feng et al demonstrated Te-doped Pd nanocrystals promoted urea synthesis by coupling CO 2 RR with electrochemical reduction of nitrite. [8] Yuan et al found a novel Mott-Schottky Bi-BiVO 4 heterostructures-enabled urea synthesis from N 2 and CO 2 , with a Faradaic efficiency increased to 12.55%. [9] However, to the best of our knowledge, no reports currently exist utilizing solar energy for urea synthesis to reduce the intensity of its operating conditions.…”

Photochemistry Journey to Multielectron and Multiproton Chemical Transformation

“…In particular, tandem catalysis is preferable to approach challenging synthetic targets, which enables multicenter collaboration and coherent bond transformations. With these joint efforts, multielectron and proton photochemistry will offer more competitive solutions to store the abundant photons (i.e., solar energy) into valuable chemical bonds at ambient temperatures and pressures, such as photocatalytic “green hydrogen” production, ammonia synthesis, , urea synthesis, as well as CH 4 activation, in place of conventional industrial processes that cause severe fossil fuel consumption and CO 2 emission. In addition, multielectron and proton photochemical reactivities will enable versatile and promising opportunities to recycle “wasted” substances such as CO 2 into value-added compounds such as C1 fuels, carboxylic compounds, and multicarbon feedstocks, maintaining carbon-neutrality for chemical manufacturing (Figure c). ,− Along this line, we are getting unprecedently close to the visions by pioneering photochemists: versatile multielectron and multiproton photochemical synthesis will not only match and even outcompete the quantum efficiency, chemo-selectivity, regio-selectivity, stereoselectivity, and scalability of natural photosynthesis but also offer energy-economic, step-economic, carbon-neutral, and value-added solutions for sustainable chemical manufacturing in the next few decades.…”

“…In particular, tandem catalysis is preferable to approach challenging synthetic targets, which enables multicenter collaboration and coherent bond transformations. With these joint efforts, multielectron and proton photochemistry will offer more competitive solutions to store the abundant photons (i.e., solar energy) into valuable chemical bonds at ambient temperatures and pressures, such as photocatalytic "green hydrogen" production, ammonia synthesis, 36,126 urea synthesis, 38 as well as CH 4 activation, 127 in place of conventional industrial processes that cause severe fossil fuel consumption and CO 2 emission. In addition, multielectron and proton photochemical reactivities will enable versatile and promising opportunities to recycle "wasted" substances such as CO 2 into value-added compounds such as C1 fuels, carboxylic compounds, and multicarbon feedstocks, maintaining carbonneutrality for chemical manufacturing (Figure 9c).…”

“…In this situation, tandem catalysis will be advantageous to collaborate light harvesting, charge transfer, proton transfer, and bond modification kinetics across broad time scales, thus facilitate consecutive multielectron and proton transformations. These efforts, along with advanced catalyst design, deeper mechanistic insights, and theoretical calculations, will boost more effective light utilization toward valuable photochemical synthetic opportunities, such as transforming abundant small molecules (e.g., H 2 O, CO 2 , N 2 ) to upgraded fuels (e.g., H 2 , CH 4 ), fertilizers (e.g., NH 3 , urea), and value-added chemicals at enhanced atom-economy, step-economy, regio-selectivity, and stereoselectivity.…”

Photocatalyzed Production of Urea as a Hydrogen–Storage Material by TiO2–Based Materials

“…Few studies propose using direct solar or radiant energy for urea synthesis by photocatalysis. One of the latest publications in this field presents the simultaneous photocatalyzed reduction of NH 3 and CO 2 on palladium nanoparticles with promising results [40]. This review analyzes a hardly explored alternative route to industrial urea synthesis: photochemical production using TiO 2 -based materials.…”