Effect of the Crystallographic Phase of Ruthenium Nanosponges on Arene and Substituted‐Arene Hydrogenation Activity

Abstract

Identifying crystal structure sensitivity of a catalyst for a particular reaction is an important issue in heterogeneous catalysis. In this context, the activity of different phases of ruthenium catalysts for benzene hydrogenation has not yet been investigated. The synthesis of hcp and fcc phases of ruthenium nanosponges by chemical reduction method has been described. Reduction of ruthenium chloride using ammonia borane (AB) and tert‐butylamine borane (TBAB) as reducing agents gave ruthenium nanosponge in its hcp phase. On the other hand, reduction using sodium borohydride (SB) afforded ruthenium nanosponge in its fcc phase. The as prepared hcp ruthenium nanosponge was found to be catalytically more active compared to the as prepared fcc ruthenium nanosponge for hydrogenation of benzene. The hcp ruthenium nanosponge was found to be thermally stable and recyclable over several cycles. This self‐supported hcp ruthenium nanosponge shows excellent catalytic activity towards hydrogenation of various substituted benzenes. Moreover, the ruthenium nanosponge catalyst was found to bring about selective hydrogenation of aromatic cores of phenols and aryl ethers to the respective alicyclic products without hydrogenolysis of the C−O bond.

Synthesis and Mechanism of Formation of Metal Nanosponges and their Catalytic and Hydrogen Sorption Properties

“…The BET surface area values have been summarized in supporting information. Since Cl − , NO 3 − , and SO 4 2− are non‐coordinating in nature, they do not have any influence on nanosponge formation . However, in contrast to the reduction of Ag(OAc) wherein we obtained Ag nanoparticles, in case of Cu(OAc) 2 , a nanoporous structure resulted.…”

“…Here we noted that ammonia borane does not reduce all of the copper salts that we employed in this work. On the other hand, sodium borohydride has been used as a reducing agent for the preparation of nanosponges, previously . Therefore, we used NaBH 4 as a reducing agent for studying the effect of counter‐anion of the metal salt substrate on the nanostructure formed.…”

“…reported that in‐situ prepared nanoparticles can be agglomerated kinetically leading to the formation of metal nanosponges . Other research groups have adopted similar methodology for the synthesis of metal nanosponges ,. In this synthetic method, NaBH 4 , a strong reducing agent has been used, which leads to rapid nucleation and growth and attachment of the nanoparticles ,.…”

Recent Advances in Heterogeneous Catalysis for Ammonia Synthesis

“…[133] Ru with fcc phase over supported catalysts is another fascinating research topic for itself, with different solutions exciting as synthesis methods. [171,172] High surface area (83 m 2 /g), Ru nanosponges with fcc crystal structure developed using a special reducing agent were superior in hydrogenation reactions. [172] Until recently, only B 5 sites in Ru were considered as active for N 2 activation.…”

“…[171,172] High surface area (83 m 2 /g), Ru nanosponges with fcc crystal structure developed using a special reducing agent were superior in hydrogenation reactions. [172] Until recently, only B 5 sites in Ru were considered as active for N 2 activation. But several Ru based catalysts with special electronic and geometrical structures such as Ru 2 Y, LaRuSi, single atom Ru in zeolite framework and Ru substituted ABO 3 perovskite, all without B 5 sites, still exhibited a significant activity in NH 3 synthesis with different pathways concluding presence of B 5 site is not always essential for development of Ru catalyst in NH 3 synthesis.…”