Academic standards are typically decided and held up by specific colleges and universities, not necessarily by their religious affiliation. Some Catholic colleges may have much higher academic standards or may be more challenging than most universities, but it isn’t a guarantee for all Catholic colleges.
Catholic colleges are private universities, and in order to give viable degrees to graduates, they must be accredited. Accreditation is done on the national and regional level. As long as they meet the standards of accreditation agencies, they are considered an “accredited college/university,� and the degrees that they award graduates are recognized by all as actual bachelor's degrees. Many companies/career fields will not accept individuals with degrees from unaccredited colleges/universities because the education is not considered up to standard.
All that to say, if a Catholic college is accredited, they have met the standard for their education for the nation and/or their specific region. Because of this, many Catholic colleges are comparable in terms of academic standards and challenge level to other colleges, private and public, with the same accreditation.
However, there are some Catholic colleges that have very high academic standards, going above and beyond the standards set for accreditation. Some Catholic colleges are Ivy league or near Ivy league, and these colleges pride themselves on their prestigious education, which means that the academic standards and challenges will be much higher.
For the most part, Catholic colleges compare relatively evenly with other colleges of the same accreditation, be that public or private colleges/universities. However, academic standards are going to be set and enforced by the individual colleges and universities, not necessarily by their category or religious affiliation. For more information on what sort of academic standards are in place at a Catholic college, inquire with the admissions department of the college(s) you are interested in.