Development and Application of Efficient Ag‐based Hydrogenation Catalysts Prepared from Rice Husk Waste

Abstract

The development of strategies for the sustainable management and valorization of agricultural waste is of outmost importance. With this in mind, we report the use of rice husk (RH) as feedstock for the preparation of heterogeneous catalysts for hydrogenation reactions. The catalysts were prepared by impregnating the milled RH with a silver nitrate solution followed by carbothermal reduction. The composition and morphology of the prepared catalysts were fully assessed by IR, AAS, ICP‐MS, XPS, XRD and STEM techniques. This novel bio‐genic silver‐based catalysts showed excellent activity and remarkable selectivity in the hydrogenation of nitro groups in both aromatic and aliphatic substrates, even in the presence of reactive functionalities like halogens, carbonyls, borate esters or nitriles. Recycling experiments showed that the catalysts can be easily recovered and reused multiple times without significant drop in performance and without requiring re‐activation.

Preparation, Characterization and Antimicrobial Properties of Nanosized Silver‐Containing Carbon/Silica Composites from Rice Husk Waste

“…Additionally, reflexes at 26.6°and 50.1° fitting to a crystallin hexagonal α‐SiO 2 phase are also present. The peak shapes for cubic silver reflexes at 38.1°, 44.3°, 64.5° and 77.5° match those of similar materials previously reported by our group, [42] which indicates the existence of a bimodal Ag crystallite phase. Beside these three phases, two weak peaks at 35.6° and 62.7° indicate the existence of cubic Fe 2 O 4 which can commonly be observed in RHA due to the high iron content in the plant [43] .…”

Highly active heterogeneous hydrogenation catalysts prepared from cobalt complexes and rice husk waste

“…Surprisingly, the addition of bases to our system (whether organic or inorganic) appears to be detrimental (Table 2), a phenomenon which we observed in other RH-based systems before. 20 When comparing the catalytic performance of the prepared materials with literature reports, they have shown to be better than, or at least comparable with most reported catalysts. 64,65 Some superior systems include those developed by the teams of Palkovits and Beller, operating at 40 °C, 36 and those by Zou and co-workers, which are very active even at room temperature.…”

“…79,80 Recently, our group developed a silver-based system also using rice husk ashes as a support, with the same selectivity. 20 Interestingly, all these systems, except the silverbased, exhibit apparent activity for kinetic product control. This does not seem to be the case for the RH based systems as no diamino species could be detected even with prolonged reaction time, higher pressure, and increased reaction temperature.…”

“…16 Recent examples include the use of catalysts made from banana peels, 17 or oyster shells, 18 for transesterification reactions, or the use of heterogeneous catalysts from rice husk (RH) for the epoxidation of limonene, 19 and the reduction of nitro groups. 20 Hydrogenation reactions are among the most important catalytic transformations in the chemical industry, as illustrated by the widely applied reduction of nitro compounds to amines. This reaction is a key transformation in the industrial-scale production of amines, 21,22 as well as in the synthesis of active pharmaceutical ingredients like the widely used paracetamol.…”

1T-MoS2catalysed reduction of nitroarenes and a one-pot synthesis of imines

“…2,[8][9][10][11][12][13][14][15][16] Habitually, most of the catalytic hydrogenations of nitroarenes use extensive transition-metal catalysts with flammable hydrogen gas. [17][18][19][20][21] The notable drawbacks of using molecular hydrogen gas as a hydrogen source are the requirements of high temperature and pressure with the help of specialized reaction vessels/setup. This proviso can be eluded using various other hydrogen sources, such as formic acid, 22,23 ammonia borane, 9,[24][25][26] silane, 27 ammonium salt, 28,29 sodium borohydride, [30][31][32][33][34] and hydrazine monohydrate, 8,[35][36][37][38] for the corresponding reduction of nitroaromatics in contrast to the conventional conditions.…”