There are only two research centers at a higher position than ICMAB: the Institute of Photonic Science (ICFO) (2nd place) and the Catalan Institute of Nanoscience and Nanotecnology (ICN2) (6th place). The Institue for Research in Biomedicine (IRB) (8th place) and the Institute for High Energy Physics (IFAE) (9th place) are also within the Top 10 Institutions.
The other places are for universities: the University of Barcelona (UB) (1st place), the Autonomous University of Barcelona (UAB) (4th place), the Pompeu Fabra University (UPF) (5th place), and the Polytechnic University of Catalonia (UPC) (10th place). The Catalan Institution for Research and Advanced Studios (ICREA) occupies the 3rd place, although the ICREA researchers are distributed in many research centers and universities accross the territory.
The table of the Top 10 Institutions in Bacelona also depicts the WFC from 2012, the change in WFC between 2012 and 2016 and the AC for 2016.

Barcelona lures scientists while Madrid is bound by bureaucracy
The Nature's article "
Spain's science rivalry" (
Nature 550,
S180–
S183 (19 October 2017);
doi:
10.1038/550S180a) compares Madrid and Barcelona, in terms of scientific quality from the data gathered for the Nature Index 2017 Science Cities report.
Barcelona seems to attract talented scientists, in large part thanks to the ICREA program, started in 2001:
In 2016, each ICREA researcher brought in almost €300,000 (US$360,000), quadrupling the amount invested in them by the institution. Indeed, almost half of the European Research Council grants to Spanish scientists over the past decade have gone to Catalonia, close to 50% of which were awarded to ICREA researchers.
According to Nature, the new research centers created by the Catalan government have favoured Barcelona's research performance:
The flexibility these centres offer in recruiting and paying staff salaries, as well as the administrative and funding support for setting up new labs, has appealed to international researchers.
ICMAB has 5 ICREA Researchers among its staff. And, although belonging to CSIC, which according to Nature is "hampered by the govenrnment's rigid employment rules and dependent on the public budget for science, which between 2009 and 2013, decreased by 32%", the ICMAB is one of the few research centers of CSIC that increases its staff. The high amount of competitive European projects granted to its researchers, and the Severo Ochoa Center of Excellence recognition, is in part responsible of its growth and success.