Pd/Mo 2 N-TiO 2 as efficient catalysts for promoted selective hydrogenation of 4-nitrophenol: A green bio-reducing preparation method Xiqiang Tian a,b , Zahid Muhammad a , Jiang Li a , Wang Sun a , Xiaoyu Niu a , Yujun Zhu a,⇑ a Key Laboratory of Functional Inorganic Material Chemistry, Ministry of Education of the People’s Republic of China, Heilongjiang University, Harbin 150080, China b Department of Food and Pharmaceutical Engineering, Suihua University, Suihua 152061, China article info Article history: Received 14 January 2020 Revised 10 August 2020 Accepted 21 August 2020 Available online 1 September 2020 Keywords: Palladium Selective hydrogenation Bioreduction 4-Nitrophenol Catalpa Fruit abstract The addition of a suitable co-catalyst is an encouraging way to enhance the catalytic performance of Pd based catalyst with low content. Herein, we describe an easy synthesis of Mo 2 N-TiO 2 with well-dispersed Mo 2 N nanoparticles through one pot evaporation-induced self-assembly and nitridation treatment method. Moreover, a green bio-reductive approach with Catalpa Fruit (CF) extract was adopted to fabricate Pd/Mo 2 N-TiO 2 catalysts for promoting selective hydrogenation of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) as model reaction. Among these Pd/Mo 2 N-TiO 2 catalysts, 0.8 wt%Pd/Mo 2 N-TiO 2 exhibits significantly high catalytic activity for selective hydrogenation of various nitrophenols and cin- nmaldehyde. Importantly, the catalytic activity of the catalyst prepared by the reduction method of the CF extract is higher than that prepared by the reduction method of NaBH 4 . A serials of characterization, including XRD, N 2 adsorption–desorption, TEM, XPS, CO chemisorption and CO-FTIR etc., was carried out to investigate the influence of the prepared method on the surface Pd species and activity. The high performance can be attributed to the specific nanostructure characteristics of the catalyst and the good synergistic effect between Pd and Mo 2 N, improving the dispersion of Pd nanoparticles atoms and the exposure of more active Pd atoms (surface Pd 0 species) on 0.8 wt%Pd/Mo 2 N-TiO 2 due to the CF extract as reductant. Ó 2020 Elsevier Inc. All rights reserved. 1. Introduction Recently, with the fast growing of the chemical industries, nitroaromatic compounds are being extensively utilized in indus- trial processes, including the manufacture of dyes, pharmaceuti- cals, pigments, pesticides and wood preservatives [1–3]. Nonetheless, due to the release in industrial effluents, nitroaro- matic compounds are mostly considered as water pollutants, which is one of the pollutants that have a serious impact on health. In particular, 4-nitrophenol (4-NP) is a ‘‘priority pollutant” because of its high toxicity, high solubility and stability in water. Moreover, U.S. Environmental Protection Agency listed 4-NP as one of top 114 organic pollutant [4–6]. In addition, the atmospheric photochemi- cal reactions of nitrobenzene and aromatic hydrocarbons with hydroxyl radicals and nitrogen oxides results in the formation of nitrophenols [7,8]. Chemical reduction of 4-NP to 4-aminophenol (4-AP) by NaBH 4 is a cost-effective method because this route can achieve high conversion efficiency with clean processing and easy operation and detection. Furthermore, 4-AP is renewed to be an available intermediate in the synthesis of various analgesic, antipyretic drugs, dye, corrosion inhibitor, photographic developer, and hair-dyeing agent etc. [9,10]. In order to promote the hydrogenation reaction of 4-NP to 4-AP, a stable and effective catalyst is necessary. Undoubtedly, noble metal-based catalysts, such as Ag, Pt, Pd, Au, Ru, etc., remain the leading role in the field of hydrogenation systems [11–16]. How- ever, noble metal catalysts have limited practical applications due to their high cost and scarcity. Moreover, it is still challenging to control the size and improve the uniform dispersion of noble metal particles on the support to minimize the probability of aggregation [17–21]. Hence, the design of a catalyst with low noble metal content and excellent catalytic performance is of great research value. For the past few years, transition metal nitrides have been researched extensively owing to their synergistic effects with noble metal in catalysis field [22–24]. Importantly, in our pre- vious works, it was found that metal nitrides could distinctively enhance the activity and selectivity of noble metal (Pt, Pd) for https://doi.org/10.1016/j.jcat.2020.08.027 0021-9517/Ó 2020 Elsevier Inc. All rights reserved. ⇑ Corresponding author. E-mail address: yujunzhu@hlju.edu.cn (Y. Zhu). Journal of Catalysis 391 (2020) 190–201 Contents lists available at ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat