Abstract:     Low-carbon economy is closely related to green development. The current analysis of the effect of carbon emission trading pilot policies on innovation incentives lacks empirical evidence at the micro-enterprise level. In this study, the carbon emission trading pilots conducted in 7 provinces and cities at the end of 2013 are used as quasi-natural experiments. Based on the patent data of A-share listed companies in China′s Shanghai and Shenzhen stock exchanges from 2009 to 2016, we use the DDD estimation method to compare the changes in the proportion of green patent applications by companies before and after the implementation of the carbon trading pilot policy, in the pilot area relative to the non-pilot area, and the high-polluting industry relative to the low-polluting industry, explores the impact of carbon trading mechanism policies on corporate green innovation activities. Furthermore, this study conducts a series of heterogeneity discussions and robustness tests, according to the types of green patents, the types of corporate ownership, the measurement standards of industry pollutants, etc., to in-depth explore how the carbon trading mechanism affects the output of corporate green patents. 
     This study finds that: (1) Compared with non-pilot areas and low-pollution industries in pilot areas, carbon trading pilot policies can increase the proportion of green patent applications by companies in high-pollution industries in the pilot areas. (2) Compared with green patents for inventions, this policy has a stronger role in promoting non-invention patents in green patents. (3) Compared with state-owned enterprises, this policy has a more significant role in promoting the green innovation level of non-state-owned enterprises among listed companies in the pilot areas. In the mechanism analysis, this study found that the carbon trading mechanism can increase scientific researchers, R&D expenditures, and the net profit margin of enterprises in high-polluting industries, which will have direct and indirect effects on the green innovation output of enterprises.
     According to the analysis results of this study, the policy recommendations are as follows: (1) Implementation of the carbon trading mechanism should be deepened. The conclusion that the carbon trading mechanism can significantly stimulate R&D and innovation of enterprises provides an empirical support for actively promoting the full launch of the carbon trading mechanism in China. In the future, the intensified implementation and more comprehensive promotion of carbon trading pilots can reduce air pollution and protect resources and environment. At the same time, it will better promote energy saving and green development of enterprises. (2) The green patent market for inventions should be developed. The carbon trading mechanism has a stronger role in promoting non-invention green patents, but the development of invention green patents cannot be ignored. Therefore, companies should further develop the invention green patent market and improve the technologically more complex and innovative inventions. The output of similar green patents will jointly promote the green development, transformation and upgrading of Chinese enterprises. (3) Differentiated carbon trading policies should be formulated. The carbon trading mechanism has a heterogeneous effect on the listed companies in the pilot area. Therefore, in the process of my country′s full implementation of the carbon trading market, the heterogeneity of different industries should be considered in many ways, and the carbon trading policies of different types of enterprises should be precisely designed. With a definite target, further improve the promotion effect of this policy on different types of enterprises. (4) Enterprises should be encouraged to improve investment in R&D. Carbon trading policies can stimulate enterprises in high-polluting industries to increase the introduction of scientific research personnel and R&D expenditures to increase their green innovation output. Therefore, relevant departments can introduce incentive policies to encourage enterprises to increase investment in scientific and technological research and development, increase the introduction of talents, and thereby increase innovation output.

Key words:  carbon trading mechanism, corporate green patent, difference-in-differences-in-differences (DDD)