捕捉信用评级虚高的信号--债券信用评级报告的文本分析

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Description
自2014年首家债券违约以来,违约金额和主体数逐年大量增加,其中不乏拥有A、AA甚至AAA评级的发债主体。投资者切实感受到债券市场的风险,因而不得不谨慎看待债券的信用评级。信用评级影响着债券的发行、市场价格以及投资者决策,然而一直以来,国内评级机构给予企业债券的评级普遍高于海外市场的相应评级;在此背景下,投资者更加关注如何识别出评级愈发虚高的债券个体。信用评级报告是支持评级结果的核心文件,也是资者了解债券的重要信息来源和进行投资决策的参考。然而,信评报告已然非常模板化,投资者很难通过报告本身来判断评级结果是否虚高。本文采用自然语言和机器学习工具分析信评报告的文本,其中应用PKUSeg进行中文分词和标注、TextRCNN进行文本分类分析、基于情感词典和机器学习预测模型共同进行文本的情感分析。研究样本涉及400多家债券发行主体和近800份信评报告,本文研究发现不同评级机构和不同档次的评级报告之间存在文本和情感因素的差异,通过抽取发生主体违约和评级下调的信评报告对差异加以验证。研究结果表明信评报告的文本分析有助于捕捉评级虚高的信号。
Date Created
2021
Agent

FeOx-Supported Platinum Single-Atom and Pseudo-Single-Atom Catalysts for Chemoselective Hydrogenation of Functionalized Nitroarenes

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Description

The catalytic hydrogenation of nitroarenes is an environmentally benign technology for the production of anilines, which are key intermediates for manufacturing agrochemicals, pharmaceuticals and dyes. Most of the precious metal catalysts, however, suffer from low chemoselectivity when one or more

The catalytic hydrogenation of nitroarenes is an environmentally benign technology for the production of anilines, which are key intermediates for manufacturing agrochemicals, pharmaceuticals and dyes. Most of the precious metal catalysts, however, suffer from low chemoselectivity when one or more reducible groups are present in a nitroarene molecule. Herein we report FeOx-supported platinum single-atom and pseudo-single-atom structures as highly active, chemoselective and reusable catalysts for hydrogenation of a variety of substituted nitroarenes. For hydrogenation of 3-nitrostyrene, the catalyst yields a TOF of ~1,500 h-1, 20-fold higher than the best result reported in literature, and a selectivity to 3-aminostyrene close to 99%, the best ever achieved over platinum group metals. The superior performance can be attributed to the presence of positively charged platinum centres and the absence of Pt–Pt metallic bonding, both of which favour the preferential adsorption of nitro groups.

Date Created
2014-12-03
Agent